GB1129962A - Improvements in or relating to the assessing of surface profiles - Google Patents

Abstract

1,129,962. Evaluating surface roughness; photo-electric graph reading. RANK ORGANISATION Ltd. Jan.18, 1966 [Jan. 18,1965; Aug.26, 1965], Nos.2166/65and36673/65. Headings G1A and G1N. The surface roughness of a machined material is measured and analysed electrically to determine the average roughness. As shown (Fig. 6), the surface is scanned by a stylus A driven across the test surface by a motor M1 through rack and pinion 4a. The output from a transducer B is fed to a galvanometer 10, whose mirror 11 reflects the light from a lamp 12 on to a film strip 3 for recording the tracer signal. The film record, comprising a contour line separating dark and clear areas, is fixed in a tank 8, and assessed at station 9, light from lamp 12 is fed through that portion of the strip located between sprockets 5a and 18, firstly to a photo-cell 17, giving a signal corresponding to the original gauge signal, and so to a number of individual photo-cells 16, the light passing through a number of lenses 15 and a light filter 15a whose opacity varies along its length in accordance with a predetermined weighting function (Fig. 8) which is symmetrical about the value measured by photo-cell 17 and with alternating positive and negative parts of diminishing amplitude. The outputs from cells 16, some of which are negative, are algebraically added to determine the mean value, which may be added to the record on strip 3. The two signals may also be combined to estimate the roughness as the deviation from the mean value. In a modification, the weighting filter 15a is replaced by electrical weighting of the output of the photo-cell 16. The tracer output may be recorded on a magnetic tape, and the photo-cells replaced by reproducing heads in association with weighted electrical circuits. In another embodiment (Fig. 15), a lamp 51 produces a slit of light across a moving belt 50 through a transparent electrode 55 fed with the gauge signal. The belt 50 is coated with a photoconductive material which is charged by the light to a voltage determined by the signal voltage on electrode 55, located downstream along the belt are capacitor electrodes 56, 57, 58 shaped in accordance with the desired weighting function, which sum the surface charge over its areas, and add the pick-up voltages algebraically to give an output signal voltage which is the required mean value. The corresponding mid-ordinate value is measured by a narrow strip electrode 59. The mean value may be obtained by feeding the gauge signal through an integrating delay network whose characteristic incorporates the weighting function.