Procedure for watching over the area in front of a lift

• US 4,742,549 A
• Filed: 10/04/1985
• Issued: 05/03/1988
• Est. Priority Date: 10/05/1984
• Status: Expired due to Term

• Current Assignee: Elevator GmbH
• Original Assignee: Elevator GmbH
• Inventors: Roschier, Nils-Robert
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): Couso, Jose L.
• Application Number:
  US06/784,642
• Time in Patent Office: 942 Days
• Field of Search: 340/550, 340/552, 340/561, 340/562, 340/568, 340/579, 340/825.37, 307/116, 307/125, 49/25, 49/28, 49/31, 324/77 B, 324/77 E, 324/78 R, 342/166, 342/179, 187/104, 382/1
• US Class Current: 382/100
• CPC Class Codes: H03K 17/943 using a plurality of optical emitters or detectors, e.g. keyboard

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.

Claims

1. 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, from which image signals suitable to be digitally processed are obtained, with a pick-up signal preprocessing means based on mutual interaction of image points from the image point pick-ups, wherein the procedure contains at least the following processing steps of the image signals, in separate image forming channels:

(a) transformation of a current of the image signal to a voltage dependent on its logarithm,

(b) conversion of the above-mentioned voltage to a first pulse signal, of which the frequency depends on the magnitude of said voltage.

(c) combining the pulse signals of the different channels with the aid of an interaction network and supplying the resulting channel-specific signals to an electric charge pump for forming a second pulse signal in a manner known in itself in the art, the frequency of said second pulse signal being over the interaction network dependent on the ratios between the frequencies of the other channels'"'"' first pulse signals, and

(d) sensing the difference between the frequencies of the channel-specific second pulse signals for resolving relative changes in intensity of the object being imaged.

2. Procedure according to claim 1, wherein the logarithmic transformation of the image signal current is carried out by observing the voltage building up across a resistor, which is proportional to the logarithm of the ratio of two currents, through a first diode being conducted a substantial part of the image signal current, and through a second diode being conducted a reference current compensating for the variations of the circuit elements, and said voltage being amplified before forming the first pulse signal.

3. Procedure according to claim 1, wherein a current of an interaction point is formed with the aid of the currents from channel-specific constant current sources belonging to the interaction network and of interaction currents passing through all capacitances.

4. Procedure according to claim 1, wherein a given number of pulses of said second pulse signal is counted channel-specifically with pulse counters starting simultaneously so that after the counter of the channel with the highest frequency has finished another counter is started, and which is allowed to count pulses up to the finishing of the counter of the channel with the lowest frequency, when the result in said second counter is compared with a given decision threshold indicating a large enough relative change in intensity of the light that has appeared in the imaging area, said result of comparison serving as instruction for a lift door opening mechanism to closing the door or to continue to keep it open.

5. Procedure according to claim 1, wherein the watch over the area in front of the lift door a lift door closing system is influenced so that on the basis of the image information received an open time of the lift door is prolonged as required.

6. A device for watching over the area in front of a lift door, said means comprising photoelectric image point pick-ups grouped for producing a one-dimensional or two-dimensional image, connected to pickup-specific image signal preprocessing channels based on electric charge pumps in mutual interaction and producing an image signal suited for digital processing, wherein each image signal processing channel comprises at least:

(a) an image signal current logarithmic transformer by the aid of which said current can be transformed into a voltage depending on its logarithm,

(b) a voltage/frequency converted by the aid of which a first pulse signal having a frequency dependent on the magnitude of said voltage can be produced.

(c) a two-stage electric charge pump known in itself in the art in which the first stage consists of a modulating circuit for the first pulse signal and of an interaction point by mediation of which the image signal processing channel of the image signal is connected to the other equivalent channels, and a second stage of a frequency oscillator, the second pulse signal formed by it having a frequency which over the interaction network dependent on mutual ratios of the frequencies of the first pulse signals of the other channels, and

(d) means for counting the frequency of said second pulse signal, for resolving relative intensity changes of the object being imaged.

7. A device according to claim 6, wherein the image signal current logarithmic transformer comprised in the means consists of a pair of diodes connected in parallel with reference to the current, of control circuits for the currents passing through said diodes and by which a substantial part of the image signal current can be directed to pass through one diode to form an information dependent on an illumination incident on the image point pick-up, while a given smaller part of the image signal current can be directed to constitute a reference current passing through the other diode and adjustable in accordance with the variations of the circuit components'"'"' characteristics, and of a resistor, the voltage established across this resistor owing to the image signal current being observable.

8. The device according to claim 6, wherein the voltage/frequency converter comprised in the means is based on the modified basic circuit, known in itself in the art, of the electric charge pump, where the input variable is a voltage, by the aid of which a variable pulse frequency can be produced.

9. The device according to claim 6, wherein the interaction network consists of channle-specific constant current sources and of capacitances connected between all channels.

10. The device according to claim 6, wherein the device comprises one pulse counter per image forming channel for counting the pulses of said second pulse signal, a counter for calculating a largest difference between the counting rates of the channels, means for comparing the count result representing said difference with a predetermined threshold value, and means for delivering a control signal, dependent on the result of comparison, further to a control system of the lift door.

11. The device according to claim 6, wherein the output of the device is so connected to a control system of the lift door that open time of the lift door can be prolonged as required on the basis of the image information received.