Patent ID: 7072032

Claim:
An automatic tracking apparatus for a reflector comprising: a surveying machine body; an illumination portion, which is disposed in said surveying machine body, and illuminates a measurement light of a modulated measurement light toward a reflector; a light receiving portion, which is disposed in said surveying machine body, and has an image sensor for receiving a reflection light image of the measurement light illuminated toward said reflector; an arithmetic device configured to calculate a position of the reflection light image from said reflector in an area of said image sensor; and a rotation mechanism, which rotates said surveying machine body such that the position of the reflection light image obtained by said arithmetic device becomes a center of the image sensor, wherein said light receiving portion is provided with a light receiving sensor, which has a smaller area than the area of said image sensor, and is disposed in a conjugated position with the image sensor on a light receiving optical axis of the light receiving portion, so as to receive a quantity of light in a vicinity area including an image center of the image sensor, and a synchronization detecting circuit which detects an output of the light receiving sensor in synchronization with the modulated measurement light, and said arithmetic device determines the reflection light image from the reflector if the synchronization detecting circuit detects that a modulated frequency of the modulated measurement light coincides with a frequency of the output of the light receiving sensor, and rotates the rotation mechanism based on the determination to track the reflector.