Beam rotation angle detecting apparatus, rotation detecting apparatus and beam rotation angle detecting method

A beam rotation angle detecting apparatus comprising:

• a light receiving portion for detecting the incidence positions of at least two beams moving on concentric circles while forming a track as a circle or an arc;
• an arithmetic system for calculating and outputting the angle between a straight line linking together at least two incidence positions detected by said light receiving portion and a predetermined reference line;
• pulse generating means for generating a pulse signal of a predetermined frequency;
• a counter for counting the pulse signal;
• selection means for successively changing over and outputting the outputs of the plurality of independent light receiving elements on the basis of the value of said counter;
• filter means for removing the signal of the predetermined frequency component from the output signal of said selection means;
• comparison means for comparing the output signal of said filter means with a predetermined value;
• detecting means for detecting the value of said counter at a changing point of the output signal of said comparison means;
• and
• arithmetic means for calculating angle information corresponding to the beam incidence position by the use of the result of the detection by said detecting means,
• wherein said light receiving portion has a plurality of independent light receiving elements continuously constructed on the circumferences of the circles on which said beams move.