| 摘要 |
PROBLEM TO BE SOLVED: To miniaturize a friction brake and to stabilize the braking force by setting the braking force so as to regulate the reverse rotation of an electric motor in its non-drive and so as to make the electric motor slidable in the reverse drive. SOLUTION: When a motor 12 is stopped, a force is added to a nut holder 22 in the direction leaving a screw shaft retaining case 18 according to the weight of a movable base or the weight of a load. Therefore, a reverse rotating force is applied to a screw shaft 20. This rotating force forms a rotating force for reversely rotating the motor 12 through a rotation transmitting mechanism 14. In the reverse rotation of the motor 12, a one-way clutch is operated to transmit the rotation to a friction plate 54. The friction plate 54 is nipped by a disc to regulate the rotation. When the braking force of the friction brake is larger than the rotating force by a load, the movable base is not lowered. The disc is nipped between a cap part and a coil spring to press the friction plate 54, so that a braking force is generated by the slide of the friction plate 54 with the disc.
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