To prevent deterioration of an infrared ray emitting diode (IRED) and to continuously perform autofocusing from the start of the projection by a projector.
When a power source is turned on, the IRED is driven in a first driving condition, and focusing is performed on the basis of an output signal from a PSD. Thereafter, the IRED is driven in a second driving condition where loads on the IRED are reduced as compared with the first driving condition, and a range-finding signal is calculated on the basis of a clamp signal, and a distance signal is calculated on the basis of the integrated range-finding signal. When a range-finding error occurs, the last range-finding result in the first driving condition is maintained as it is, and the range-finding in the first driving condition is not redone. In such the situation that the normally acquired distance signal changes from the last distance signal in the first driving condition by the amount equal to or exceeding a prescribed threshold, the range-finding in the first driving condition is redone. Except for the redoing of the range-finding, the range-finding is continued in the second driving condition until the power source is turned off.
COPYRIGHT: (C)2008,JPO&INPIT
Shigeru Iijima
Kobayashi Hideyoshi
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