Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1986-01-09
1988-01-05
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
250221, 250210, 340555, H01J 4014
Patent
active
047178205
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a device for detecting movable objects within a limited detection area.
DESCRIPTION OF THE PRIOR ART
In connection with, for example, automatically operated doors and burglar alarms, there is a demand for a device for detecting movable objects, primarily human beings, but also e.g. shopping trolleys in department stores and beds in hospitals. Several such devices are already in existence today, and the effect of these devices is based on ultrasonics, microwave technique, optoelectronics. The ultrasonic detectors may be based on the Doppler effect or on echo recordings. The microwave technique is usually based on the Doppler effect. The group of optoelectronic detectors comprises, for example, photocell systems of the reflecting and refractive type and video cameras.
It is an object of the present invention to provide a device operating with visible light for detecting movable objects, said device being intended to provide identical detection of varying objects, warm as well as cold. The device should be indifferent to environmental variations, apart from movements, for example acoustic/optical variations, and provide for simple signal processing and also determination of the speed of the detected object. A further object of the invention is to provide such a device of this type as is capable of determining the direction of movement of the detected object.
DESCRIPTION OF THE INVENTION
The present invention relates to a new and improved optical device operating with visible light and adapted to detect movable objects within a limited detection area. The device comprises an arrangement of a number of juxtaposed photosemiconductors uniformly distributed on two bridge branches in an electric bridge circuit, such that two adjacent photosemiconductors are included in separate bridge branches. If the photosemiconductor arrangement receives an image of the detection area, the bridge is largely in balance, independently of the intensity of the surrounding light and the reflectivity of stationary surfaces within the detection area. If an object is moving across the area, its image will be projected on the photosemiconductors alternately in one and the other bridge branch. In this manner, the bridge will provide a low-frequency alternating voltage, regardless of whether the object is darker or lighter in relation to its surroundings or background. By full-wave rectification, there is obtained a unipolar output signal of double frequency, the magnitude of which is proportional to the speed of the object within the detection area.
If there are arranged, for detecting movable objects within a limited detection area, several devices of the above-mentioned type, with mutually different orientations of their semiconductor arrangements, the output signals of the devices will provide, in combination, information about the direction of movement of a detected object within the detection area. Such a multi-device arrangement may be used to advantage in, for example, the application of the basic idea of this invention to automatic door operation, such that the door is operated, for example opened, only if the movement of the object has one or more predetermined directions, for example towards the door.
The image of the limited detection area must not be thrown or projected directly onto the photosemiconductors, but individual picture elements of the area may be conducted to the photosemiconductors by means of light guides, such as fiber optical light guides. Examples of photosemiconductors suitable for the purpose of this invention are photodiodes, phototransistors and photoresistors.
BRIEF DESCRIPTION OF THE DRAWINGS
Thc invention will be described in more detail below, reference being had to an embodiment chosen by way of example and illustrated in the accompanying drawing in which
FIG. 1 shows an arrangement of photoresistors in the device,
FIG. 2 shows a circuit diagram of the device, and
FIG. 3 shows a circuit diagram of a rectifier comprised by the devic
REFERENCES:
patent: 3191048 (1965-06-01), Cowen
patent: 3793523 (1974-02-01), Desvignes et al.
patent: 3803572 (1974-04-01), Campman
LandOfFree
Device for detecting movable objects does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for detecting movable objects, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for detecting movable objects will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-9814