| 摘要 |
PURPOSE:To detect exactly an obstacle even in case when a foreign matter such as snow or mud, etc. adheres by detecting the receiving level of a side lobe wave propagated to a receiving element from a transmitting element, and controlling the transmitting gain or the receiving sensitivity of an ultrasonic wave. CONSTITUTION:A side lobe wave extracting circuit 10 receives an ultrasonic receiving signal passing through an amplifier 5, eliminates an obstacle detecting signal contained in said signal, extracts only a side lobe wave signal, and supplies it to a level deciding circuit 11. The circuit 11 compares a voltage level Vs of the side lobe wave signal with a voltage level Vso of a normal time, and in case of Vs<Vso, it is decided that a sensitivity drop due to adhesion of a foreign matter, etc. is generated, an amplified gain switching control signal is sent to a switching circuit 12, and the gain of the amplifier 5 is controlled so as to become Vs=Vso. As a result, a receiving voltage level of the side lobe wave signal is kept constant, the sensitivity drop is compensated by the increase of amplified gain, and an obstacle is detected with the same accuracy as the normal time. |
