Automatic tracking apparatus for reflector

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.