Collision avoidance method and system

DETAILED DESCRIPTION The present invention is directed to a collision avoidance system including a reader device attached to a moving vehicle such as a construction vehicle and a tag device, which is worn on the body of a construction pedestrian.
The reader device periodically transmits an ultrasonic pulse which, if the pedestrian is within a predetermined range, is received by the tag device.
The tag device, in response to the reception of the ultrasonic pulse from the reader device, transmits an RF response pulse to the reader device.
The reader device determines the distance of the pedestrian from the reader device based on the elapsed time between the transmission of the ultrasonic pulse and the reception of the RF pulse.
Varying modes of alarm may be activated, based on the distance of the pedestrian from the reader device.
A visual and/or audible alarm device is located proximate the operator of the vehicle.
It should be noted that for the purposes of this writing, it is assumed that the tag device is worn by a pedestrian and the reader device is mounted on a moving vehicle.
However, a tag and reader pair may be installed on any number of objects, of any type, which one wishes to protect from collisions.
Furthermore, any number of tags may be installed on multiple objects within the fields of any number of readers, to support collision avoidance between those objects with readers and those objects with tags.
It is further noted that the present invention describes ultrasonic transmissions in air, as it is expected this will be appropriate for the largest number of applications.
However, operation of the system in other transmission media, such as through smoke, debris, or underground, is possible with straightforward changes to account for ultrasonic transducer interfacing to the medium and to account for the speed of sound in the medium.
According to one embodiment of the invention, a presence detection system is disclosed, including a reader device attached to a first body, and a tag device attached to a second body