1. Field of the Invention
The present invention relates to a method and an apparatus for sensing a human body that is available, for instance, in an automatic door or the like.
2. Description of the Prior Art
In an automatic door, approach of a human body to the door is sensed, and in response to the sensing of a human body a door opening/closing signal is generated to actuate the door to open and close, and to that end, as a method and an apparatus for sensing a human body, various kinds of methods and apparatus have been known in the prior art.
For example, a method and an apparatus for sensing a human body, in which a projector for projecting infra-red rays and a photo-sensor adapted to receive infra-red rays reflected by a floor surface and a human body are provided and the photosensor generates a sense signal when it senses variation of the amount of reflection of infra-red rays, have been known.
However, these heretofore known methods and apparatus had the following shortcomings:
(1) If rays of sunlight should momentarily enter the photo-sensor as reflected by any moving body, then a sense signal would be incorrectly generated, and hence sometimes, a door may malfunction. PA1 (2) If the infra-red rays projected from the projector should momentarily enter the photo-sensor as reflected by falling snow, then a sense signal would be incorrectly generated, and hence sometimes, a door may malfunction. PA1 (3) Under the condition where a human body stands still, it cannot be sensed.
More particularly, since the amount of reflection from a floor surface of the irradiated infra-red rays would change according to variation in time of a radiation efficiency of the projector and according to variation of the floor surface condition, in the event that a level of the amount of reflection of the infra-red rays is simply used for determination of sensing of a human body, minute variation in time of the level itself of the amount of reflection would be caused by the above-mentioned variation of the amount of reflection, hence it is necessary to inhibit sensing of that variation, consequently a level difference of a minute amount of reflection becomes hard to be senced, and so a sensing distance cannot be chosen long.
In order to resolve this problem, a method in which the amount of variation of the reflection amount is sensed rather than the reflection amount itself and a sense signal is provided depending upon the amount of variation, that is, a method of differential operation type, may be employed, but if such type of method is employed, in the case where a human body stands still, the human body cannot be sensed because the reflection amount does not vary.