Apparatus for changing the speed

An apparatus for changing the rotational speed of a mechanism comprising:

• an input shaft for receiving an input rotation,
• a plurality of planetary gear units, each having a sun gear, a plurality of planetary gears meshing with the sun gear, an internal gear meshing with the planetary gears and a carrier for rotatably supporting the planetary gears, the planetary gear units being positioned from first to last, respectively in an axial direction toward an output side of the apparatus around the input shaft, the carrier of a unit being connected to the sun gear of a next unit, the sun gear of the first unit being connected to the input shaft,
• an output rotor rotatably mounted on the input shaft without preventing relative rotation thereof,
• a casing containing the input shaft and all the planetary gear units, the casing rotatably supporting the input shaft and the internal gear of the last of the planetary gear units and fixing the internal gears of the other planetary gear units,
• a rotating disc fixed to the input shaft near the output rotor,
• a disc-contacting device for bringing the rotating disc into contact with the output rotor,
• an internal gear stopping device for stopping rotation of the internal gear being rotatably supported by the casing, and
• a connecting cylinder being pierced by the input shaft for connecting the carrier of the last planetary gear unit with the output rotor, wherein the internal gear stopping device and the disc-contacting device are operable in a complementary manner such that:
• the internal gear stopping device is engaged while the disc-contacting device is disengaged and the disc-contacting device is engaged while the internal gear stopping device is disengaged, the output rotor rotates at a high speed when the disc-contacting device engages the rotating disc with the output rotor, and the output rotor rotates at a low speed when the internal gear stopping device is engaged, and wherein the internal gear stopping device comprises:
• a solenoid having a plunger which extends or retracts in an axial direction,
• a stopper piece attached to the plunger,
• a guide for guiding the stopper piece in the axial direction, and
• a bracket for fixing the solenoid to the casing,
• an outer surface of the internal gear of the planetary gear unit being permitted rotation in the casing includes an outer toothed surface, such that:
• when the solenoid is excited to one direction, the stopper piece is brought into engagement with the outer toothed surface of the internal gear and the internal gear is stopped;
• and
• when the solenoid is excited to the other direction, the stopper piece disengages from the outer toothed surface and the internal gear can rotate freely.