MONITORING SYSTEM FOR A PREDETERMINED FIELD OF VIEW

摘要

A lift control system includes a spatial filter for producing a signal having various features, a discriminator for discriminating one or more features of the signal, and for producing a control signal when at least one of the features discriminated falls in a predetermined range, and active devices connected to the discriminator. The spatial filter is defined by a semi-spherical bowl having a plurality of openings or by a poly-face prism which is made from a plano-convex lens with its curved face so polished or cut as to have a plurality of flat faces.