Actuator, manufacturing method of actuator, light scanner and image forming apparatus
An actuator includes a light reflection part having light reflectivity, a movable part having the light reflection part and being rotatable around a rotation center axis, a pair of connection parts connected to the movable part, and a support part that supports the pair of connection parts, and each of the connection parts includes a pair of beam members, a distance between the pair of beam members gradually increases from a first surface side toward a second surface side of the movable part when seen from a direction in parallel to the rotation center axis of the movable part, and given that a distance between ends at the first surface side of the pair of beam members is W 1 and a thickness of the pair of beam members in a thickness direction of the movable part is t, the following expression (1) is satisfied. w 1 < t tan 54.73 ° ( 1 )
1. An actuator comprising:
a movable part rotatable around a rotation center axis, the movable part having movable top and movable bottom surfaces opposite to each other, the movable top surface extending in a first direction;
a pair of connection parts connected to the movable part, the pair of connection parts having connection top and connection bottom surfaces; and
a support part that supports the pair of connection parts, wherein
the movable part is in a cross shape in a plan view,
the movable bottom surface has a recess, a recess bottom surface of the recess is located between the movable top surface and the movable bottom surface, and a permanent magnet is located on the recess bottom surface,
each of the connection parts includes a pair of beam members,
a beam distance between the pair of beam members gradually increases from the connection bottom surface toward the connection top surface when seen from a direction in parallel to the rotation center axis of the movable part,
each of the beam members has inner and outer side surfaces between the connection top surface and the connection bottom surface, and one of the inner and outer surfaces having two inclined surfaces that incline with respect to the first direction, the two inclined surfaces extending in the same direction, and
given that a first distance between ends at the connection bottom surface of the pair of beam members is W 1 and a thickness of the pair of beam members in the thickness direction of the movable part is t, the following expression (1) is satisfied
w
1
<
t
tan
54.73
°
.
(
1
)
2. The actuator according to claim 1 , wherein, given that a second distance between ends at the connection top surface of the pair of beam members is W 2 , the following expression (2) is satisfied
t
<
tan
54.73
°
2
(
w
1
+
w
2
)
.
(
2
)
3. The actuator according to claim 1 , wherein the movable part, the support part, and the pair of connection parts are formed by anisotropic etching of a silicon substrate having a plate surface formed by a (100) crystal surface of silicon.
4. The actuator according to claim 3 , wherein each of the beam members has a sectional shape of a parallelogram when seen from the direction in parallel to the rotation center axis.
5. The actuator according to claim 4 , wherein an outer shape of the sectional shape of each of the beam members is formed by a pair of top and bottom sides along the (100) crystal surface of silicon and the inner and outer side surfaces along a (111) crystal surface of silicon.