LIGHT BEAM CAPTURING AND TRACKING METHOD AND LIGHT BEAM CAPTURING AND TRACKING APPARATUS

PURPOSE:To improve tracking properties by switching open loop control to close loop control after light beam is made to be closer to an optical axis under open loop control. CONSTITUTION:An input signal (d) to a driving part 1 is connected with a terminal 15 side to form open loop control and a driving angle ordering value signal (b) is given to the driving part 1. The driving part 1 is moved toward the aiming light beam (a) and its opitcal axis is properly direct. When the optical axis 1 is set to direct within a directional precision range, the light beam a can be captured in a light receiving plane 6 of a tracking error angle detecting sensor 3. The capturing error angle signal (c) at the position 17 at 0 time (t) when the light beam a is detected at first by the sensor 3 is detected. The signal (c) is added to the signal b by a computer 5 to drive the driving part 1 and its optical axis is set again to direct toward the light beam a. After the optical axis re-directing work is completed, a switching apparatus is connected with a contact point 14 side to compose a close loop. By this operation, the light beam a moves from the position 17 to the position 18 on the light receiving plane 6 of the sensor 3. Consequently, the light beam a can be drawn quickly to the center (optical axis) of the light receiving plane 6.