Electric actuator
The rotary motion of a ball screw shaft is converted into the rectilinear motion by a ball spline nut provided integrally with displacement members by the aid of an attachment section. Involute splines are engraved on outer circumferential surfaces of spline pistons connected to the displacement members. The spline pistons are slidably meshed with a splined bore of the involute splines formed on an inner wall surface of a frame. The attachment section is displaceable in a longitudinal direction of the frame by the aid of the splined bore and the spline pistons.
1. An electric actuator comprising:
a frame;
a rotary driving source which is disposed inside or outside said frame;
a feed screw shaft which is connected to a drive shaft of said rotary driving source for receiving rotary driving force from said rotary driving source;
a displacement mechanism which is engaged with said feed screw shaft, which converts rotary motion of said feed screw shaft into rectilinear motion, and which is displaceable in an axial direction of said feed screw shaft; and
a spline guide mechanism which is connected to said displacement mechanism, which guides said displacement mechanism in said axial direction of said feed screw shaft, an which absorbs loads applied to said displacement mechanism in a substantially vertical direction, in a circumferential direction about a center of an axis of said feed screw shaft, in a circumferential direction about a center of a horizontal line substantially perpendicular to said axis of said feed screw shaft, in a circumferential direction about a center of a vertical line substantially perpendicular to said axis of said feed screw shaft, and in a direction obtained by compositively combining said directions,
wherein said spline guide mechanism includes a splined bore which has a plurality of adjacent splines provided in a longitudinal direction formed over an entire inner wall circumferential surface of said frame, and a pair of spline pistons each of which has a plurality of adjacent spline teeth, formed over an entire outer circumferential surface, to be fitted to said splined bore.
2. The electric actuator according to claim 1 , wherein said displacement mechanism includes a ball spline nut which is screw-engaged with a ball screw shaft by the aid of a ball bearing, a pair of displacement members which abut against both ends of said ball spline nut and which are connected to said ball spline nut, and an attachment section which is attached to said pair of displacement members.
3. The electric actuator according to claim 2 , wherein said pair of spline pistons are provided while being separated from each other by a predetermined spacing distance at ends of said pair of displacement members in a displacement direction, and said pair of spline pistons are meshed with said splined bore which is formed on an inner wall surface of said frame.
4. The electric actuator according to claim 1 , wherein said splined bore has involute spline.
5. The electric actuator according to claim 1 , wherein said pair of spline pistons have involute splines.
6. The electric actuator according to claim 1 , wherein said displacement mechanism includes a ball spline nut which is screw-engaged with a ball screw shaft by the aid of a ball bearing and which is connected between said pair of spline pistons, and a cylindrical guide member which is connected to one spline piston and which is movable back and forth with respect to an end of said frame by making displacement along said splined bore formed in said frame.
7. The electric actuator according to claim 1 , wherein a gap exists between sliding surfaces of said spline teeth and said splines, when the spline teeth of said pair of spline pistons are meshed with the splines of said splined bore.
8. The electric actuator according to claim 7 , wherein said gap is about 0.003mm.
9. The electric actuator according to claim 7 , wherein a high-viscosity grease is charged to said sliding surfaces, between said splined bore and said spline pistons, said high-viscosity grease having a kinematic viscosity within a range of 1000 to 10000 cSt.
10. The electric actuator according to claim 9 , wherein said high-viscosity grease has a kinematic viscosity of 2200 cst or 9850 cSt.
11. The electric actuator according to claim 1 , wherein said spline pistons are formed of one of polyoxymethylene, polyimide, and ultra-high molecular weight polyethylene.
12. The electric actuator according to claim 1 , wherein a chamfering angle of 15° 20° is formed on respective ends of the spline teeth of said spline pistons.
13. The electric actuator according to claim 1 , wherein said frame has a longitudinal slot, further comprising an attachment section attached to said displacement mechanism and protruding into said longitudinal slot, said attachment section being displaceable in said slot in unison with said displacement mechanism.