US 12,292,311 B2
Absolute encoder
Kaoru Nishiguchi, Nagano (JP); Yasuo Osada, Nagano (JP); and Takahiro Ohara, Nagano (JP)
Assigned to MINEBEA MITSUMI Inc., Nagano (JP)
Appl. No. 17/758,474
Filed by MINEBEA MITSUMI Inc., Nagano (JP)
PCT Filed Dec. 25, 2020, PCT No. PCT/JP2020/048982
§ 371(c)(1), (2) Date Jul. 7, 2022,
PCT Pub. No. WO2021/140974, PCT Pub. Date Jul. 15, 2021.
Claims priority of application No. 2020-002883 (JP), filed on Jan. 10, 2020.
Prior Publication US 2023/0024876 A1, Jan. 26, 2023
Int. Cl. G01D 5/14 (2006.01); G01D 5/04 (2006.01)
CPC G01D 5/145 (2013.01) [G01D 5/04 (2013.01); G01D 2205/26 (2021.05); G01D 2205/28 (2021.05)] 2 Claims
OG exemplary drawing
 
1. An absolute encoder configured to identify an amount of rotation of a main shaft over multiple rotations, the absolute encoder comprising:
a first drive gear configured to rotate according to rotation of the main shaft;
a first driven gear configured to mesh with the first drive gear;
a second drive gear provided coaxially with the first driven gear and configured to rotate according to rotation of the first driven gear;
a second driven gear configured to mesh with the second drive gear; and
a magnet provided at a tip end side of the first drive gear, and an angle sensor configured to detect a rotation angle of the first drive gear provided with the magnet in response to a change in a magnetic flux generated from the magnet, wherein
a first magnetic pole portion of a first polarity and a second magnetic pole portion of a second polarity different from the first polarity are formed adjacent to each other in the magnet as viewed from an axial end surface of the magnet,
the first magnetic pole portion and the second magnetic pole portion are formed adjacent to each other in a radial direction with a center of the magnet in the radial direction as a boundary,
the first magnetic pole portion and the second magnetic pole portion are formed adjacent to each other in the axial direction with a center in the axial direction as a boundary,
a magnetic interference reduction member formed of a magnetic material is provided on an outer peripheral surface of the magnet in the radial direction,
wherein the magnetic interference reduction member surrounds an entire outer peripheral surface of the magnet in the radial direction and is in contact with the outer peripheral surface; and
the first drive gear is provided on a radial outer side of a cylindrical member, the cylindrical member having a magnet holding portion, wherein the magnet and the magnetic interference reduction member are accommodated within the magnet holding portion.