| 摘要 |
When the reflectance of an object to be measured is low and when the distance is far to the object, these conditions are discriminated and the distance is measured with a clamp signal being set at a low level, thereby enhancing distance measurement accuracy. First distance measurement is carried out with the clamp signal being set at a high level. When the first distance value is a value over a predetermined distance, second distance measurement is then carried out with the clamp signal being set at the low level (e.g., S56). Then it is determined whether the second distance value D2 is larger than a set value B (e.g., S60). When the second distance value D2 is larger than the set value B, the clamp signal is set to the high level (e.g., S64) and third distance measurement is carried out (e.g., S68). When in S60 the second distance value D2 is not larger than the set value B on the other hand, the clamp signal is set to the low level (e.g., S82) under certain conditions and the third distance measurement is carried out (e.g., S86).
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