GB955045A - Improvements relating to optical indicating devices - Google Patents

Abstract

955,045. Photo-electric indicating. arrangements. VERWALTUNGESELLSCHAFT DEN WERKZEUGMASCHINEN-FABRIK OERLIKON April 13, 1962 [May 16, 1961], No.14358/61. Heading G1A. In an arrangement for determining the positional relationship between relatively moving parts, for example of a machine, a portion of a scale on one part is optically projected on to a directly viewed screen on the other and also on to a bank pf photo-cells arranged to give output pulses as each subdivision of a set sub-dividing the scale intervals is passed. In Fig. 1 the two parts are indicated at 1 and 2 and it is assumed that the part 2 is fixed and extends some distance in a direction perpendicular to the paper. In a recess it carries a shaped glass bar 3 bearing graduation marks 4. The part 1, assumed movable, carries a light source 9 and collimating lens system 10 directing a beam of light on to bar 3 in which it is twice internally reflected by surfaces 5 and 6 and then illuminates a portion of scale 4. A magnified image of a portion of the scale including a single mark 4 is formed on frosted glass plate 12 having scale markings thereon and may be viewed through lens 14. Each mark 4 has a thickened extension whose image is formed below plate 12 and in the same plane. This image lies across a bank of photo-diodes arranged as shown in Fig. 3. All the photo-diodes in the upper row (16) are arranged in series in one arm of a bridge and all the photodiodes in the lower row (17) are in series in an adjacent arm of the bridge. With five cells in each row, the distances between the centres of the extreme cells equal to the mark spacing, and a mark width equal to the centre to centre spacing of adjacent cells the bridge will be balanced ten times as movement takes place for one mark to occupy the same position on the field as was occupied by an adjacent mark. Thus if pulses are produced by a suitable circuit each time balance is achieved the number of pulses represents the number of tenths of the scale units moved by the movable member. A counter may be provided to indicate the position reached to the nearest tenth of a scale unit. Instead of dark marks being projected on to the bank of photo-diodes the marks may be bright and the intervals between them dark. In this arrangement the photo-diodes are arranged in parallel in the arms of the bridge circuit (Figs. 4 and 8, not shown). It is possible also to arrange the two rows of photo-diodes side by side such that adjacent marks of the scale co-operate with the different rows as indicated in Fig. 5.