PURPOSE: To enable correction of light according to a board thickness so as to be incident effectively into a light receiver when the board thickness of a light transmitting plate material is changed,. by providing a parallel mirror, a driving section, a controller section and the like.
CONSTITUTION: As a board thickness of a glass plate 10 changes, the optical path of a transmission light 17 is dislocated. When the transmission light 17 with a dislocated optical path falls into a CCD camera 25, the current position thereof 17 is detected and inputted into a control section 31. The control section 31 calculates the size and the direction of the dislocation in the current position of the transmission light from the original position and a driving section 30 is controlled by a control signal to turn a parallel mirror 29 so that the transmission light 17 is adjusted to reach the original position of a light receiver D1. When an absolute value of a deviation between the current and original positions is larger than the minimum thereof, the control signal is outputted to a driving section 30. Moreover, the driving section 30 turns the mirror 29 o the basis of the control signal from the control section 31, thereby enabling correction of the transmission light 17 so that is reaches the original position.
TANAKA KENJI
ABE JUNICHI
MIYANO MITSUO
YASKAWA DENKI SEISAKUSHO KK
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