INTERFERENCE AVOIDANCE DEVICE FOR USE IN A SENSOR SYSTEM

The invention provides an apparatus and method to confirm or deny the presence of an object within the scan area of an ultrasonic sensing system by requiring that any object be identified on at least two consecutive scans of the sensing system and using scan energy patterns which occur at irregular repetition times to selectively reject spurious direct or reflected signals present in the area. A generator of predetermined pattern burst of ultrasonic energy is arranged to produce one such burst of ultrasonic energy and a timing signal is coupled thereto so as to apply timing signals to cause production of the bursts. The timing signal source produces timing signals only according to a varying pattern whereby separation between adjacent signals meet certain present parameters. The energy patterns are applied to a transmitter which applies them to a scan area whereby the echo or returned energy from an object in the scan area is received and stored. The return from the next sequential burst is also stored and compared to the first. If the two agree the presence of the object is confirmed. If the two do not agree, then the contents of storage one is destroyed and the storage used to store the next sequential burst is compared. Failure to confirm means that an object was not present or that the object moved out of the scan area before its presence could be confirmed or a false signal was present, or one of a number of reasons, but no object is present.