| 摘要 |
PROBLEM TO BE SOLVED: To provide a position retaining mechanism for a load member, a valve drive and its driving method without requiring a complex control device. SOLUTION: The position retaining mechanism for the load member has a motor 3 and a transfer gear train 5 and retains the position of the load member 6 in a position where an output shaft 4 is rotated against the force of the load member 6 connected to the output shaft 4. The transfer gear train 5 has a planet gear 35 and a driven gear 40 which includes an outer toothed section 41 and inner toothed sections 42a and 42b comprising toothed portions along the revolution locus of the planet gear 35. When the planet gear 35 meshes with the outer toothed section 41, the driven gear 40 is rotated to rotate the output shaft 4; when the planet gear 35 mesh with the inner toothed sections 42a and 42b, the driven gear 40 is not rotated but held in its position to retain the position of the load member 6. The planet gear 35 and the inner toothed sections 42a and 42b are brought out of mesh with each other to cancel retention of the position.
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