Absolute sensor

An absolute sensor comprising:

• a high speed rotational shaft;
• a planetary gear mechanism for reducing a high rotational speed delivered from the high speed rotational shaft;
• a low speed rotational shaft which is aligned coaxially with the high speed rotational shaft and to which is delivered a reduced speed rotation from the planetary gear mechanism;
• a high speed side encoder for detecting a rotational speed or rotational angle of the high speed rotational shaft;
• and
• a low speed side encoder for detecting a rotational speed or rotational angle of the low speed rotational shaft;
• the planetary gear mechanism has a fixed sun internal gear, a front stage planetary gear, a rear stage planetary gear which rotates integrally with the front stage planetary gear, and an output sun internal gear engaged with the rear stage planetary gear;
• and
• the front stage and rear stage planetary gears are rotatably supported by an eccentric shaft portion formed on the high speed rotational shaft and are maintained in a condition engaged with the fixed sun and output sun internal gears, and the output sun internal gear is connected to the low speed rotational shaft,
• whereby an absolute rotational angle of the low speed or high speed rotational shaft is detected based on outputs of the high speed side and low speed side encoders.