Patent GB-1260534-A (GB)
Title: Surface finish inspection device
IPC: G01N21/89
Filed: 1969-04-23
Abstract: 1,260,534. Inspecting surfaces photoelectrically. PHILCO-FORD CORP. April 23, 1969 [May 21, 1968], No.20691/69. Heading G1A. In a device for analyzing the smoothness of the finish of a surface 10 of a body of material, a plurality of illuminated areas are projected on to the surface by means of an illuminated reticule 20g and the surface is scanned along a path including its illuminated area by a photo-cell 36 and rotating mirror 30, the photo-cell output being a scan signal whose instantaneous amplitude is proportional to the brightness of the portion of the path being scanned. As shown, radiation from a plurality of fluorescent tubes 16 passes through a reflector/diffuser 18 and openings in the reticule 20 to illuminate the surface of a blank 10. As mirror 30 rotates, movement of each face of the mirror results in successive portions along the entire length of blank 10 being focussed on photocell 36 by way of plane mirror 26 and lens system 32, this scan being repeated for succeeding faces of mirror 30, while each blank is moved continuously in the direction of the arrow. Thus, the output from photo-cell 36 is a varying signal Fig.3 (not shown) whose maxima correspond to the illuminated portions of the blank. In a similar way, a reference signal of constant peak-to-peak amplitude is provided by photo-cell 38, whose focused field of view scans across the openings in a vertical reticule 22 illuminated by reflection of radiation from fluorescent tubes 16 in the reflector/ diffuser 18. The peak-to-peak amplitude of the output from photo-cell 36 varies, illuminated portions of blank 10 that contain a blemish producing a lower voltage signal than illuminated high-gloss portions, and this output is first amplified, then full-wave rectified, before being passed to a low-pass filter (44). This filter gives a D.C . voltage output proportional to its A.C. input voltage, and this output is fed to a reversescaled D. C. voltmeter which is calibrated directly in micro-inches of surface roughness. The above mentioned rectified signal is also fed to an AND gate (50), which also receives a train of sharp pulses corresponding to maxima of the reference signal and produced by rectifying and pulse-shaping means Fig. 2 (not shown). The AND gate thereby produces a sharp pulse corresponding to each illuminated portion of the blank that contains a blemish, and these pulses are converted to square pulses by a monostable multi-vibrator (72). If a predetermined number of these "blemish" pulses occurs within a certain time period, the threshold voltage of a latch circuit (70) is exceeded, and a count of "1" is accordingly registered on a counter (78). In this way, the number of blemishes per blank may be counted for quality control purposes, and the output of the latch circuit may be also used to actuate means for marking blanks of inferior surface finish. An inhibiting gate (54) and further pulsing circuitry ensures that a 3" region at each end of each blank is not investigated, since these portions are subsequently cut off, and a plate photo-cell 14 is provided to reset the latch circuit and counter whenever a blank passes out of the scanned region.