Absolute encoder and method for determining rotation amount

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.

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.

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.