| 摘要 |
PURPOSE:To contrive simplification and cost reduction by reducing the number of parts, by winding the intermediate part of a belt not substantially stretching but having flexibility in the longitudinal direction thereof around the peripheral surface of either one of a drive shaft and a piece to be driven. CONSTITUTION:A belt 18 is singly wound around the outer peripheral surface 17A of a drive shaft 17 in the vicinity of the central part 18A thereof and the narrow part 18C provided to one side of the belt 18 is inserted in the slot 19 provided to the other side thereof and both end part sides of the belt 18 are extended to opposite directions to each other along the peripheral surface 14A of a piece 14 to be driven and fixed to the piece 14 to be driven. If the drive shaft 17 revolves by an angle theta, the belt 18 is involved in the drive shaft 17 at one side thereof corresponding thereto while the other side of the belt 18 is paid out. By this operation, the piece 14 to be driven having the end part of the belt 18 fixed thereto also revolves by a predetermined angle phi. According to this revolution, a diffraction lattice 10 also revolves by the angle phi and the wavelength of light emitted from an emitting slit changes by the amount corresponding to the angle phi.
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