GB1400841A - Apparatus for determining the profile of a plane or cylindrical surface - Google Patents

Abstract

1400841 Photo-electric profilometers FRANCE MINISTER FOR EQUIPMENT & HOUSING 26 May 1972 [28 May 1971] 24907/72 Heading G1A A profilometer comprises a light source arranged in such a way that as the beam scans the surface it is reflected to a point on the input element of a photo-multiplier device depending on the distance of the surface from a reference plane, the photo-multiplier device being arranged to scan the input element to produce successive signals representing the position of the incident light beam. As shown, Fig. 1, the light from a laser 1 is scanned across a surface R by means of a rotating prism 5. The surface is simultaneously scanned by rotating mirror 21 and the reflected beam is directed through an image correcting prism 37 which is rotated at half the speed of mirror 21, an interference filter 44 to reduce the effects of sunlight, and a lens 45, on to the photo-cathode 53 of a photo-multiplier device. The electrons emitted by the photo-cathode are deflected by coils 68 so that the position of the light beam can be determined by the deflection required for the electron beam to pass through an aperture into the multiplier section. A co-ordinate transformer 67 ganged to the mirror 21 provides an output which is compared with a 41 level generator 60 to provide a start pulse at 41 spaced positions across each scan. The output of a clock 56 is applied to divider 57 to produce 40KHz pulses which are differentiated (58) to produce 25Á S pulses which are applied to scanning circuit 24 to deflect the electron beam section of the photo-multiplier. The scanning circuit 24 is also provided with an input from analyzer 67 which is ganged to the mirror to correct for the change in optical path length as the mirror rotates. The pulses are also applied to a counter 63 which is stopped when an output signal is produced by the photo-multiplier the count being related to the position of incidence of the radiation on the target which itself depends upon the distance of the surface R from the axis of rotation of the mirror. The output of counter 63 is applied to a memory 64 and is gated (65) to a magnetic memory with continuous erasure. The apparatus is mounted on vehicle which moves along a roadway and is kept a constant distance from the edge by an optical system. A pendulum accelerometer is used to detect and correct for the angle of the laser relative to the transverse horizontal line. The optical axis of the apparatus is inclined at an angle to the longitudinal axis of the vehicle to compensate for the skew scan resulting from its forward motion. The apparatus may also be adapted for cylindrical surfaces by making the axes of the mirror and prism coincident and angling the mirror to receive the reflected radiation. The scan may be produced by a rotating laser instead of by the rotating prism 5.