| 摘要 |
Each of plural detection units performs a signal transmission-reception operation responding to at least one of a plurality of kinds of operation timing signals repeated at a predetermined periodicity. The number of continuous reception times of the reflection signal is counted and used to determine obstacle detection when the number of counts is larger than or equal to a predetermined value. The transmission-reception operations are controlled by an operation timing signal having a periodicity shorter than the predetermined periodicity.
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