Patent ID: 7281445

Claim:
A gear speed reducer comprising: an actuator for producing rotational drive power in response to an electric signal supplied thereto; a drive shaft rotatable by the rotational drive power produced by said actuator; a speed reducer mechanism for transmitting the rotational drive power from said drive shaft and having cycloidal gears for reducing speed of the rotational drive power; an output shaft disposed coaxially with said drive shaft, for outputting the rotational drive power whose speed is reduced by said speed reducer mechanism; and a rotation holding mechanism for limiting angular displacement of said output shaft which has been angularly displaced a predetermined angle, between an initial position and a terminal position when the electric signal supplied to said actuator is interrupted, wherein said rotation holding mechanism comprises: an engaging hole in a shape of an elongate hole formed along a circumferential direction of said rotation holding mechanism; an engaging pin inserted in said engaging hole; a first rotary disk coupled to said speed reducer mechanism for rotation in unison therewith; a second rotary disk disposed adjacent to said first rotary disk and engaging said first rotary disk via said engaging pin; and springs for biasing said first rotary disk and said second rotary disk in respective directions to rotate about their axes, and wherein said first rotary disk, said second rotary disk and said springs are disposed coaxially, and wherein when said first rotary disk is displaced by a predetermined angle with respect to said second rotary disk under resiliency of one of said springs, relative displacement of said first rotary disk and said second rotary disk in a rotation direction is limited by said engaging pin movable only in and along said engaging hole.