GB1376742A - Position resolvers - Google Patents

Abstract

1376742 Detecting position MARCONI CO Ltd 26 Oct 1971 [16 Jan 1971] 2223/71 Heading G4H The position of a member movable over a co-ordinate array of strips is determined by detecting movement of the member by an optical sensor. In the embodiment of Figs. 1 and 2, in which lines are painted, etched or scratched on or wires are positioned on or embedded in for example a glass plate 1, the member is a light pen 4 and the optical sensor comprises two photo-cells 5, 6; 7, 8 for each co-ordinate direction X, Y. The photo detectors are connected to circuits 10, 11, 14, 15 arranged to detect the direction of movement in accordance with which detector in each pair is first energized as a line is crossed by the pen, the circuits pulsing add or subtract inputs of X, Y counters to give binary coded counts representing the position of the member. In the embodiment of Fig. 3 (not shown) the lines comprise strips reflecting (for the X direction), blue and green light and (for the Y direction), green and red light. The pen comprises two bundles of light fibres, one leading to a light source and one to photo detectors responsive to blue, green and red light. The detectors are connected to logic circuitry so that as in the embodiment of Figs. 1 and 2, the amount and sense of movement may be represented by the count in two counters. In a modification of this embodiment the lines consist of strips reflecting green and all light and red and all light so that only two photo detectors are necessary. Instead of utilizing two bundles of light fibres, light may be transmitted from a source (20, Fig. 10, not -shown), through a semisilvered mirror (53) on to a light guide (18) connected to the movable member and light from the guide is reflected by the mirror to a photo detector assembly (21). The bundle may consist of a central fibre surrounded by six fibres placed at the corners of a hexagon, the six outer fibres being used for illumination and the inner fibre for carrying the reflected light to the detectors. Dichroic filter mirrors may be used to separate the colours in the reflected light. In an alternative embodiment (Fig. 13, not shown), each line is of coded form comprising a stripe (57) reflecting all light and a plurality of stripes (58-61) reflecting (for the X direction) red light and (for the Y direction) green light. The first and last stripes (47, 61) are wider than the rest. The strips may be so positioned that as they are scanned the pulses between the wide pulses represent the position of the member in binary form.