GB994357A - A method of and apparatus for tracing an optically discernible boundary applicable to inspection and testing of articles - Google Patents

Abstract

994, 357. Inspecting screws photo-electrically. G. K. N. GROUP SERVICES Ltd. Feb. 9, 1962 [Nov. 9, 1960], No. 38415/60. Headings G1A and G1M. [Also in Division G4] A method of tracing a boundary, such as the outline of a wood screw, comprising making a light ray incident upon the boundary and setting up relative motion between the ray and the boundary and controlling the curvature of the relative motion in accordance with the modulation of the light ray. Locking on to the object to be inspected. Wood screws 14, Fig. 1 are dropped through a channel 13. When no screw is in the field of view, the spot on a cathode-ray tube CRT. 1 is incident on a frusto-conical annular mirror 25 and light is reflected to photomultipliers 26, the output of which defocuses the spot. Thus an enlarged spot S, Fig. 5, circulates around mirror 25. When a screw enters the field of view the spot will trace down one side and up the other, each time it encounters the screw. During this tracing, photomultipliers 26 are in darkness, and the spot S is small and sharply focused, and this ensures that when the screw is completely within the field of view the spot S will detach itself from the mirror 25 and repeatedly trace the screw outline. Outline tracing system. The spot S after partial eclipse by a screw or the mirror 25 falls upon a photomultiplier V 1 which provides an error signal Œe when the spot is more or less than half eclipsed. The error signal e varies the frequency of an oscillator 17 to give an output Vcos (#t + #) where # = #edt. This output is mixed with a signal Vsin wt from an oscillator 18 to produce signals including components of cos # and sin # which are integrated and applied to the deflection plates of CRT. 1. The curvature of the spot path is thus greatest to one hand when the spot is eclipsed, to the other hand when the spot is not eclipsed, and zero when the spot is semi-eclipsed. Optical recognition of good and bad objects. The deflection signals applied to CRT. 1 are also supplied to a second CRT. 2, Fig. 12. The signal to the Y plates being passed through a filter having a time constant such that it passes the tracing signal, but not signals due to the motion of the screw through the channel 13. This results in a non- translating image of the screw outline which may be subject to rotation. The image is focused on a mask 42 rotating with a frequency large compared with possible image rotation, but small compared with the frequency of tracing. When the image and the mask coincide, the photomultiplier arrangement 46 sends a pulse to a reject control circuit 47. Circuit 47 is primed by a signal from amplifier 27, Fig. 1, when the screw enters the field of view and operates a reject device 48, such as an air blast or a paint marker unless neutralized by a recognition signal within a preset time. Electrical recognition of good and bad objects. Alternatively to this optical system, the deflection signals for CRT. 1 may be recorded on a magnetic drum 49, Fig. 14, which signals are then picked off by heads 51a, b, c, at points corresponding to selected points on the screw. These signals are amplified or attenuated at 53a, b, c, and fed to a summing circuit 52 to provide a recognition signal. The magnetic drum may be replaced by a delay circuit such as a delay line.