摘要 |
PURPOSE:To enable the highly precise detection of a ground speed at all times by method wherein sensitivity patterns of a plurality of light-detectors are varied symmetri cally from the central parts thereof to the longitudinal direction in relation to the direction of transfer of an image. CONSTITUTION:Light-receiving lattices 109 and 110 are so combined alternately as to be paired with each other and are arranged continuously, while they are so patterned that the light-receiving area of each of the them increases gradually in the longitudinal direction, becomes maximum in the center and then decreases gradually. By shaping a space filter 1 to be protuberant on both sides in this way the quantity of the light taken in the filter 1 increases gradually and then decreases gradually even when the direct-current intensity of a reflected light varies sharply with a sharp change in the circumstances of a road surface. Therefore a low-frequency component obtained through differential processing of signal of the filter 1 and superposed on an output of a differential amplifier becomes so small that it can be neglected. As the result, the missing of a central frequency component in a zero cross detector is eliminated, and thus an instantaneous state wherein a ground speed can be measured when the circumstances of the road surface changes sharply can be prevented from occurring.
|