Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-02-09
1990-11-27
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
2502221/214RC, 340556, G01V 904
Patent
active
049738372
DESCRIPTION:
BRIEF SUMMARY
This invention relates to proximity detector arrangements. Particularly, but not exclusively, the invention relates to proximity detectors which are used to control the opening and closing of automatic doors such as those employed at supermarkets or large office buildings.
Automatic door installations are known which include means for ensuring that the doors cannot close on a person standing in the doorway thereby causing discomfort or injury. Some arrangements include means for detecting the presence of a person in the doorway and one common known method makes use of a single magic eye beam projected across the door opening at a height of approximately 11/2 feet. When the beam is broken the doors cannot be closed. Other devices commonly make use of capacitive detectors for detecting undulations of the human body in front of the doorway whilst ignoring the relatively flat slam-post of the door frame by balance bridge techniques. Capacitive detectors are usually operated in bridge networks but have a number of problems. For example, the framework of the doorway and the edge of the door frame need to be parallel in order to maintain a balanced bridge condition. Secondly capacitive detectors are affected by moisture and humidity and temperature changes. Thirdly wear on the door installation may cause vibration and jitter which can again lead to false detection due to imbalance of the bridge.
These types of detectors are used only as safety devices for preventing unwanted closing of the doors but they are not capable of functioning as general door operating devices. Door operating devices are known which employ microwave type sensors and also passive infra-red type sensors. These operate by detecting movement of a body within a zone close to the door. When the sensor senses movement within that zone the doors are opened. The passive infra-red devices operate by sensing undulations in the amount of heat from a body reflected to a infra-red sensor which occurs as the person traverses the detection zone. The microwave type devices employ transmitters and receivers and operate on the Doppler principle where the reflected frequency and the transmitted frequency are summed, the difference between the two usually being in the audio frequency range. This undulation is detected and the rate of undulation is proportional to the speed of movement of the person in the detection zone.
Passive infra-red devices have a number of problems particularly when used in conjunction with automatic doors. Since they are heat detecting devices they are susceptible to gusts of wind, thermals, heat curtains etc. They can also be adversely effected by incandescent lamp radiation from for example vehicle headlamps or street lighting. Also other thermal changes can lead to false detection problems.
Microwave devices operate reasonably well as door actuators but suffer from safety defects The main problem with microwave devices is that the zone into which the microwave energy is transmitted has to be projected slightly away from the moving doors since otherwise the receivers tend to detect radiation from the doors themselves. Thus as the doors are closing they can cause a reflection of microwave energy leading to re-opening of the doors and hence an oscillatory motion of the doors. Another problem with microwave devices is their sensitivity to rainwater, moving folliage and other moving objects such as pieces of paper. Furthermore microwave proximity detectors can be triggered by radiation from transmitters such as taxi radios, fluorescent lighting and other similar devices. Also because the beam has to be projected slightly away from the doors which the proximity detector is controlling there is a dead space or zone immediately in front of the doorway and this can cause problems with slow moving persons e.g. invalids moving with a walking frame. When such a person moves into the detection zone they are sensed and the doors will open. If they stop the doors will then close but be re-opened when further movement is sensed. Immediately in fro
REFERENCES:
patent: 3197656 (1965-06-01), Kintner
patent: 3644917 (1972-01-01), Perlman
patent: 4027154 (1977-05-01), Flint
patent: 4068222 (1978-01-01), Treviranus
patent: 4075507 (1978-02-01), Pauli et al.
patent: 4166948 (1979-09-01), Steffen
patent: 4319332 (1982-03-01), Mehnert
patent: 4479053 (1984-10-01), Johnston
patent: 4799044 (1989-01-01), Masters et al.
Electrosense Limited
Nelms David C.
LandOfFree
Proximity detectors with dual-speed tracking circuitry does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Proximity detectors with dual-speed tracking circuitry, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Proximity detectors with dual-speed tracking circuitry will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1033507