GB1160824A - Method and apparatus for Checking the Evenness of Annular Surfaces - Google Patents

Abstract

1,160,824. Photo-electric investigation of annular surfaces. COMPAGNIE DE SAINTGOBAIN. April 27, 1967 [April 27, 1966], No. 19386/67. Heading G1A. [Also in Division G4] An annular surface such as that at the top of a bottle is investigated for any unevenness by photoelectric scanning apparatus. One embodiment of a suitable scanning arrangement is shown in Fig. 1. The bottle 11, whose surface 23 is to be investigated, is positioned with this surface against a reference plate 12 using the rig of Fig. 2 (not shown). The scanning light beam is formed by lenses 16 and 18, and a rotatable prism 17, directing the beam on to the reflecting surface 32 of a ring 19 of transparent acrylic resin. The beam then passes where possible during its circular movement, through the gap between face 23 and the reference plate 12 to a central conical reflector 34, from which the beam is directed to a photo-cell 37 by means of prism 35. The output of the cell 37 is a continuous waveform representative of the unevenness around the annular face 23. Measurement of the Fourier series coefficients of this waveform can give detailed information as to the degree and general form of the unevenness. Measurement of particular coefficients requires adaptation of the scanning apparatus. For example, the formation of two scanning beams, 180 degrees apart, using a double prism (17 17<SP>1</SP>, Fig. 5, not shown), enables the second Fourier coefficient (A 2 ) to be measured by analysis of the cell output, this coefficient being characteristic of a "saddle" shaped deformation of the surface 23. As an alternative to the ring 19 and prism 34, rotating mirrors may be used. A second embodiment of the scanning system is described with reference to Fig. 4 (not shown), in which the bottle (11) is placed in an inverted position on a reference plate (12), the scanning beam is directed radially outwards from a rotating semi-reflecting mirror (17), and the photo-cell (37) moves around a circle with the scanning beam. A fixed photo-cell (46) may be used as a reference cell to correct for periodic variations in the intensity of the scanning beam. Alternatively, the reference cell is omitted and a further scanning cell (37<SP>1</SP>) is located opposite the first (37), an extra scanning mirror (17<SP>1</SP>) being provided, Fig. 6 (not shown). The sum of the cell outputs gives the second coefficient (A 2 ), and the difference, the first coefficient (A 1 ), representing the angle between the face 23 and the reference plate. To measure the third coefficient (A 3 ) representing a more complicated surface defect, three cells at 120 degrees apart are used. The circuit for amplifying the output of the detector(s), Fig. 8a (not shown) includes a chopping transistor (52) by which a squarewave oscillator output is modulated with the detector signal, various amplifier and filter stages and a demodulator. Instead of electrical modulation, a flashing light source or a chopped light beam may be used. The final waveform can then be investigated using an oscilloscope, (62, Fig. 8b, not shown), or its peak voltage, giving the maximum value of the shaping fault, measured by a peak voltmeter (61). The slope at any instant is measured using a differentiating circuit and the differentiated signal applied to a logic circuit, Fig. 8c (not shown) for indication as being within one of five ranges or sorting into five groups. The logic circuit comprises an input stage (10) comprising trigger circuits (101-105), a memory stage (20) comprising five memory cells (201-205) made up of parts of NOR circuits, a selector stage of five NAND circuits and an indicator stage (40). The input voltage is applied to a potentiometer (100). Each trigger (101-105) compares the voltage from its tapping of the potentiometer with a reference voltage (+) and if at any time during the measurement cycle it is greater than this, it switches to state 1. This state is recorded in the corresponding memory cell (201-205). The selector stage selects the first memory cell non- energized and accordingly lights the corresponding indicator lamp of the array (401-405).