Importance

Loading Importance Indicators...

Abstract

A procedure for watching over the area in front of a lift door, of said area being formed with the aid of one-dimensionally or two-dimensionally grouped photoelectric image point pick-ups, image signals suitable to be digitally processed, with a pick-up signal preprocessing means based on mutual interaction of the image points. With a view to obtaining a lift door monitoring system with good resolution in a wide lighting range, the design taught by the invention contains, at least, the following features for processing the pickup-specific image signals: (a) transformation of the image signal current to a voltage dependent on its logarithm, (b) conversion of the above-mentioned voltage to a first pulse signal, (c) combining the pulse signals of the different channels with an interaction network and supplying the resulting channel-specific signals to an electric charge pump for forming a second pulse signal of which the frequency is, over the interaction network dependent on the ratios between the frequencies of the other channels' first pulse signals, and (d) sensing the differences between the frequencies of the channel-specific second pulse signals for resolving the relative changes in intensity of the object being imaged.

Loading the Abstract Image...

First Claim