Absolute encoder and method for determining rotation amount

1. An absolute encoder for determining a rotation amount of a main shaft over a plurality of rotations, the absolute encoder comprising:

at least one rotary body rotating together with a rotation of the main shaft;

a magnet rotating integrally with the rotary body; and

a plurality of rotary sensors detecting magnetic poles of the magnet to output detection signals having sinusoidal waveforms, each sinusoidal waveform having a different phase, wherein:

the at least one rotary body includes a first rotary body rotating integrally with the main shaft and a third rotary body rotating together with a rotation of the first rotary body,

the absolute encoder further comprises a first angular sensor to detect a rotational angle of the first rotary body,

the magnet is arranged in the third rotary body,

the at least one rotary body includes a second rotary body arranged between the first rotary body and the third rotary body,

the absolute encoder further comprises a second angular sensor to detect a rotational angle of the second rotary body,

the second rotary body reduces a rotational speed at a first speed reduction ratio with respect to the first rotary body,

the third rotary body reduces a rotational speed at a second speed reduction ratio with respect to the second rotary body,

a mechanism for transmitting the rotation of the first rotary body to the second rotary body includes an intermediate rotary body, the intermediate rotary body reducing a rotational speed at a third speed reduction ratio with respect to the first rotary body, and

the second rotary body reduces a rotational speed at a fourth speed reduction ratio with respect to the intermediate rotary body.

2. The absolute encoder according to claim 1 , wherein

the rotational angle of the first rotary body is determined according to a detection result of the first angular sensor,

a rotational frequency of the first rotary body is determined according to a detection result of the second angular sensor and the detection signals from the plurality of rotary sensors, and

a rotation amount of the first rotary body is determined according to the determined rotational angle of the first rotary body and the determined rotational frequency of the first rotary body.

3. The absolute encoder according to claim 1 , wherein

the mechanism for transmitting the rotation of the first rotary body to the second rotary body includes a worm mechanism having a worm gear part and a worm wheel part.

4. The absolute encoder according to claim 3 , wherein

the worm gear part is provided on the intermediate rotary body.

5. The absolute encoder according to claim 4 , further comprising

an urging member to urge to hold the intermediate rotary body in a rotational axis direction of the intermediate rotary body.

6. The absolute encoder according to claim 1 , wherein

a rotational axis of the second rotary body is provided in parallel to a rotational axis of the third rotary body, and

the first rotary body is provided between the rotational axis of the second rotary body and the rotational axis of the third rotary body.

7. An absolute encoder for determining a rotation amount of a main shaft over a plurality of rotations, the absolute encoder comprising:

at least one rotary body rotating together with a rotation of the main shaft;

a magnet rotating integrally with the rotary body; and

a plurality of rotary sensors detecting magnetic poles of the magnet to output detection signals having sinusoidal waveforms, each sinusoidal waveform having a different phase, wherein:

the at least one rotary body includes a first rotary body rotating integrally with the main shaft and a third rotary body rotating together with a rotation of the first rotary body,

the absolute encoder further comprises a first angular sensor to detect a rotational angle of the first rotary body,

the magnet is arranged in the third rotary body,

the at least one rotary body includes a second rotary body arranged between the first rotary body and the third rotary body,

the absolute encoder further comprises a second angular sensor to detect a rotational angle of the second rotary body,

the second rotary body reduces a rotational speed at a first speed reduction ratio with respect to the first rotary body,

the third rotary body reduces a rotational speed at a second speed reduction ratio with respect to the second rotary body,

the second rotary body includes another magnet rotating integrally with the second rotary body, and

when a space is divided into two regions by a plane perpendicular to a rotational axis of the second rotary body and including a rotational axis of the first rotary body,

the another magnet is arranged in the region of the two regions, in the region the magnet being not arranged.

8. An absolute encoder for determining a rotation amount of a main shaft over a plurality of rotations, the absolute encoder comprising:

a first acquisition mechanism acquiring a rotational angle of a first rotary body rotating integrally with the main shaft;

a second acquisition mechanism acquiring a rotational angle of a second rotary body, the second rotary body reducing a rotational speed at a first speed reduction ratio with respect to the first rotary body, the second rotary body reducing a rotational speed at a fourth speed reduction ratio with respect to an intermediate rotary body, the intermediate rotary body reducing a rotational speed at a third speed reduction ratio with respect to the first rotary body;

a third acquisition mechanism detecting magnetic poles of a magnet, the magnet reducing a rotational speed at a second speed reduction ratio with respect to the second rotary body, and acquiring a plurality of detection signals having sinusoidal waveforms, each sinusoidal waveform having a different phase;

a first determination element determining a rotational frequency of the first rotary body according to the acquired rotational angle of the second rotary body and the acquired detection signals; and

a second determination element determining a rotation amount of the main shaft according to the acquired rotational angle of the first rotary body and the determined rotational frequency of the first rotary body.

9. A method for determining a rotation amount of a main shaft over a plurality of rotations, the method comprising:

acquiring a rotational angle of a first rotary body rotating integrally with the main shaft;

acquiring a rotational angle of a second rotary body, the second rotary body reducing a rotational speed at a first speed reduction ratio with respect to the first rotary body, the second rotary body reducing a rotational speed at a fourth speed reduction ratio with respect to an intermediate rotary body, the intermediate rotary body reducing a rotational speed at a third speed reduction ratio with respect to the first rotary body;

detecting magnetic poles of a magnet, the magnet reducing a rotational speed at a second speed reduction ratio with respect to the second rotary body, and acquiring a plurality of detection signals having sinusoidal waveforms, each sinusoidal waveform having a different phase;

determining a rotational frequency of the first rotary body according to the acquired rotational angle of the second rotary body and the acquired detection signals; and

determining a rotation amount of the main shaft according to the acquired rotational angle of the first rotary body and the determined rotational frequency of the first rotary body.