| 摘要 |
<p>PURPOSE:To attain smooth operation changeover with simple configuration by devising the mechanism such that a lock device is moved between a restricted position and a restriction release position by a cam device in interlocking with 1st and 2nd gears and the position is regulated till a worm is moved to a prescribed position on the way of movement from the restriction release position to the restriction position. CONSTITUTION:A moment of worms 16a, 16b in a direction almost orthogonal to their drive shafts is minimized by an action of an escape angle alpha in the lock state of a lock member 24. For example, on the way of changeover, when a lock section 24b of the lock member 24 overrides a box 17, sure drive control is realized with a comparatively weak torque and sure operation control is attained with a drive motor having a comparatively small torque. Then picture hysteresis is provided to a guide from the restriction release position to the position restriction and vice versa for the lock member 24 to obtain a margin of operation control and the operation changeover control with high reliability is attained.</p> |
