Patent GB-1395800-A (GB)
Title: Method and system for inspecting the surface quality of a workpiece
IPC: G01N21/954
Filed: 1972-06-27
Abstract: 1395800 Photo-electric flaw detectors BENDIX CORP 27 June 1972 [16 July 1971]  29994/72 Heading G1A The surface quality of a workpiece is inspected by measuring the intensity and shape of a beam of radiation modulated by reflection from the surface and comparing these measurements with corresponding reference values to determine the presence and severity of any surface flaw and the smoothness of the surface respectively. As shown, Fig.1, the inside surface of a tubular workpiece 12 is inspected by scanning probe 46 containing a lens 47 and a mirror 48 which projects a beam 21 from laser 18 through an aperture 50 on to the internal surface of the workpiece from which it is reflected back along the probe and is separated by a beam splitter 52. The beam is divided into two parts by a second beam splitter 54 one part passing via a reflector 66 and a lens 70 to a photo-detector 70 which measures the intensity of the beam, the other part passing via lens 56 and chopper wheel 60 to a second detector 58 which is used to determine the shape of the reflected beam. The probe is rotated by means of a motor 39 and is mounted on a slide driven by rotor 31 for movement axially along the workpiece. The movement of the probe is controlled by command signals generated by a computer, the motors being provided with positional feedback outputs to indicate when an instructed movement has been completed, which is also utilized to perform calculations on the measurements. The intensity signal from photo-cell 70 is analyzed by means of high and low pass filters feeding a comparator to determine when a change in intensity occurs, this information being applied via line 90 to the computer to inhibit the generation of scanning commands and perform the measurement calculations when a flaw is detected. The analysis circuit 74 also combines the outputs of the filters and converts the signal to digital form for application over line 92 to the computer where it is compared with a reference value. The curvature of the workpiece surface is determined by means of chopper wheel 60 which rotates with the probe and has two slits 62, 64. Each slit in turn progressively increases and then decreases the effective field of view of detector 58 the output signal of which is analyzed to determine its second order time differential which is a measure of the shape of the scanned surface. The output of the shape analyzer 76 is also applied as an input to the computer where it is compared with a reference value. A photo-cell 72 is arranged outside the workpiece so that it produces an output when the probe moves across an aperture 74 in the workpiece to provide an inhibiting signal which prevents the change in intensity occurring at this point from being interpretted as a flaw. The flaw data is stored so that the computer can determine whether a series of flaw readings are in fact due to the scanning of a single large flaw. The computer determines whether or not any flaw is within pre-set acceptable limits and provides an output to an indicator 112. The intensity reference value may be determined by scanning a predetermined distance along the workpiece and taking the intensity value as the reference providing it remains constant.