| 摘要 |
PURPOSE:To prevent mis-detection of ranges for a device in which the range to an obstacle is detected by ultrasonic wave pulses by detecting smaller one out of ranges based on the time difference between transmission and reception of ultrasonic wave pulses and based on running ranges. CONSTITUTION:When a car moves backward approaching an obstacle D and the range between the car and the obstacle D reaches the first reference range, a passing pulse is sent from a reference range passing pulse generator 7. Then, a counter 9 counts running ranges of the car based on range signals from a running range sensor 8. An addition-subtraction circuit 10 subtracts the range data of the counter 9 from the first reference range, and sends the output to a range selection circuit 11, which compares the output from the addition-subtraction circuit 10 with the range data to the obstacle which are output from a range detector 29 of a range detection circuit 2, and it outputs the smaller range data out of the two to actuate a range indicator 3 and a warning unit 4. |
