PROBLEM TO BE SOLVED: To make fine adjustment of the vertically directed refraction of the radiated light precisely and easily and prevent a long stretching mirror from breakage by coupling a step motor through a torsion bar with the shaft of a fixing member on the same axis. ;SOLUTION: When a geared step motor 15 is operated, its torque is transmitted to the shaft 7 of each fixing frame 3 through a torsion bar 19. Because the torque is buffered by the resiliece of the torsion bar 19, no unreasonable load of bending moment will act on a long stretching mirror 1 even though the two fixing members 3, 3 rotate round the axis of the shaft 7 which is borne by an outer frame 8 through bearings 10. The refraction of the vertical component of the radiated light can be fine adjusted easily by performing feedback control through utilization of the curvature characteristic value in longitudinal direction of the mirror 1, and thus the mirror 1 can be precluded from breakage.;COPYRIGHT: (C)1997,JPO
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