Concentric multi-axis actuator
A concentric double axis actuator has a two-stage cross roller bearing, and a preceding-stage actuator and a subsequent-stage actuator which are linked in tandem. The front end of a subsequent stage rotary output shaft of the subsequent actuator, said subsequent stage rotary output shaft passing through a hollow section of the preceding-stage actuator and projecting forward, is linked and fixed to an inner ring of the two-stage cross roller bearing, and the inner ring functions as a subsequent-stage rotary output member. The output rotary side of the preceding-stage actuator is linked to an middle ring of the two-stage cross roller bearing, which functions as a preceding-stage rotary output member. The rotary output element of each stage is supported by the two-stage cross roller bearing, and surface oscillations of the rotary output member of each stage can be minimized, and the moment stiffness of the members can be increased.
1. A concentric multi-axis actuator ( 1 ) comprising:
a multi-stage cross roller bearing ( 2 ), a preceding-stage actuator ( 3 ) arranged coaxially to a rear side of the multi-stage cross bearing ( 2 ), and a subsequent-stage actuator ( 4 ) arranged coaxially to a rear side of the preceding-stage actuator ( 3 ), wherein
the preceding-stage actuator ( 3 ) has a preceding-stage hollow section ( 5 ) extending through a center thereof along a direction of an axis ( 1 a );
the subsequent-stage actuator ( 4 ) has a subsequent-stage rotary output shaft ( 6 ) extending forward through the preceding-stage hollow section ( 5 );
the multi-stage cross roller bearing ( 2 ) has an outer ring ( 11 ), a middle ring ( 12 ) arranged concentrically to an inside of the outer ring, an inner ring ( 13 ) arranged concentrically to an inside of the middle ring, an annular outside track ( 14 ) of rectangular cross section formed between the outer ring ( 11 ) and the middle ring ( 12 ), a plurality of outside rollers ( 15 ) rollably inserted within the outside track ( 14 ), an annular inside track ( 16 ) of rectangular cross section formed between the middle ring ( 12 ) and the inner ring ( 13 ), and a plurality of inside rollers ( 17 ) rollably inserted within the inside track ( 16 );
the middle ring ( 12 ) is a preceding-stage rotary output member rotationally driven by the preceding-stage actuator ( 3 ); and
the inner ring ( 13 ) is a subsequent-stage rotary output member fixed to the subsequent-stage rotary output shaft ( 6 ), and
wherein the preceding-stage actuator ( 3 ) has a preceding-stage motor ( 31 ) and a preceding-stage strain wave gear reducer ( 32 );
the preceding-stage strain wave gear reducer ( 32 ) has a preceding-stage reducer housing ( 34 ), a preceding-stage rigid internal gear ( 35 ) fixed coaxially to an inside of the preceding-stage reducer housing, a preceding-stage flexible external gear ( 36 ) of silk hat shape arranged coaxially to an inside of the preceding-stage rigid internal gear, a preceding-stage wave generator ( 37 ) fitted in an inside of the preceding-stage flexible external gear, and a center through hole ( 37 a ) formed in the preceding-stage wave generator ( 37 );
the preceding-stage reducer housing ( 34 ) is fixed to the outer ring ( 11 ), the preceding-stage flexible external gear ( 36 ) is fixed to the middle ring ( 12 ), and the preceding-stage wave generator ( 37 ) is fixed to a hollow motor shaft ( 31 a ) of the preceding-stage motor ( 31 ), the hollow motor shaft extending through the center through hole ( 37 a ) of the preceding-stage wave generator;
the subsequent-stage actuator ( 4 ) has a subsequent-stage motor ( 41 ) and a subsequent-stage strain wave gear reducer ( 42 );
the subsequent-stage strain wave gear reducer ( 42 ) has a subsequent-stage reducer housing ( 44 ), a subsequent-stage rigid internal gear ( 45 ) fixed coaxially to an inside of the subsequent-stage reducer housing, a subsequent-stage flexible external gear ( 46 ) of silk hat shape arranged coaxially to an inside of the subsequent-stage rigid internal gear, a subsequent-stage wave generator ( 47 ) fitted in an inside of the subsequent-stage flexible external gear, and a center through hole ( 47 a ) formed in the subsequent-stage wave generator ( 47 );
the subsequent-stage housing ( 44 ) is fixed to a motor housing ( 43 ) of the preceding-stage motor ( 31 ), the subsequent-stage flexible external gear ( 46 ) is fixed to an rear end of the subsequent-stage rotary output shaft ( 6 ); and the subsequent-stage wave generator ( 47 ) is fixed to a motor shaft ( 41 a ) of the subsequent-stage motor ( 41 ), the motor shaft extending through the center through hole ( 47 a ) of the subsequent-stage wave generator.
2. The concentric multi-stage actuator ( 1 ) according to claim 1 , wherein a roller size of the inside rollers ( 17 ) are smaller than a roller size of the outside rollers ( 15 ), and a roller center (L 2 ) of the inside rollers ( 17 ) is positioned at an offset along the direction of the axis ( 1 a ), with respect to a roller center (L 1 ) of the outside rollers ( 15 ).
3. The concentric multi-stage actuator ( 1 ) according to claim 2 , wherein an offset amount (Δ) of the roller center (L 2 ) of the inside rollers ( 17 ) with respect to the roller center (L 1 ) of the outside roller ( 15 ) is in a range of one-half of a track width of the inside track ( 16 ) to one-half the sum of a value of this track width and a track width of the outside track ( 14 ).
4. The concentric multi-stage actuator ( 1 ) according to claim 2 , wherein the offset amount (Δ) is one-half of the track width of the outside track ( 14 ).
5. The concentric multi-stage actuator ( 1 ) according to claim 2 , wherein a thickness of the middle ring ( 12 ) in a radial direction from a circular inside peripheral face to a circular outside peripheral face thereof is at least twice a thickness of the outer ring ( 11 ) in a radial direction from a circular inside peripheral face to a circular outside peripheral face thereof.
6. The concentric multi-stage actuator ( 1 ) according to any one of claims 2 to 5 , wherein the outside track ( 14 ) and the inside track ( 16 ) are formed in the outer ring ( 11 ), the middle ring ( 12 ), and the inner ring ( 13 ), at positions closer to one side surfaces thereof than the other side surfaces thereof, and roller insertion holes ( 12 f , 13 f ) are formed in the one side surfaces of the middle ring ( 12 ) and the inner ring ( 13 ), and are sealed with stoppers ( 18 , 19 ).
7. The concentric multi-axis actuator according to any one of claims 1 to 5 , wherein the subsequent-stage actuator ( 4 ) has a subsequent-stage hollow section ( 7 ) extending through a center thereof, the subsequent-stage rotary output shaft ( 6 ) is a hollow shaft, and the inner ring ( 13 ) is formed with a center through hole, and the subsequent-stage hollow part ( 7 ), the hollow part of the subsequent-stage rotary output shaft ( 6 ) and the center through hole of the inner ring ( 13 ) constitute a hollow part extending to pass through along the direction of the axis ( 1 a ).
8. The concentric multi-axis actuator according to claim 6 , wherein the subsequent-stage actuator ( 4 ) has a subsequent-stage hollow section ( 7 ) extending through a center thereof, the subsequent-stage rotary output shaft ( 6 ) is a hollow shaft, and the inner ring ( 13 ) is formed with a center through hole, and the subsequent-stage hollow part ( 7 ), the hollow part of the subsequent-stage rotary output shaft ( 6 ) and the center through hole of the inner ring ( 13 ) constitute a hollow part extending to pass through along the direction of the axis ( 1 a ).