Strain wave gear device
A strain wave gear device includes: an internal gear; a wave generator; a flex gear including an outer gear and a first annular portion integrally formed with the outer gear of the same material; and an outputter that rotates together with the flex gear and includes a second annular portion facing against the first annular portion in a radial direction centered on an axis. The second annular portion is provided with a transmission tooth protruding radially while the first annular portion is provided with a recess to receive the transmission tooth. The recess is circumferentially wider than the transmission tooth and tolerates relative circumferential displacement of the flex gear with respect to the outputter. Transmission pairs, each including the transmission tooth and the recess, are circumferentially arranged.
1. A strain wave gear device, comprising:
an internal gear including an inner gear formed along an inner peripheral surface of the internal gear;
a wave generator including a cam that rotates around an axis in accordance with a rotation input;
a flex gear including an outer gear having a ring shape, formed along an outer peripheral surface of the flex gear, and having a smaller number of teeth than that of the inner gear, an inner peripheral side of the flex gear being fitted around the wave generator; and
an outputter that rotates relative to the internal gear in conjunction with the flex gear, wherein
the cam has N poles, N being an integer of 2 or greater, positioned at equal intervals in a circumferential direction centered on the axis and causes the outer gear to engage with the inner gear at N positions,
the flex gear includes a first annular portion that is formed of the same material as the outer gear and integrally formed with the outer gear, the first annular portion being positioned closer to the outputter in a direction along the axis than the outer gear is,
the outputter includes a second annular portion that faces against the first annular portion in a radial direction centered on the axis,
one of the first annular portion and the second annular portion is provided with a transmission tooth that protrudes in the radial direction while the other of the first annular portion and the second annular portion is provided with a recess to receive the transmission tooth,
the recess has a width along the circumferential direction that is wider than that of the transmission tooth and tolerates relative displacement in the circumferential direction of the flex gear with respect to the outputter, and
a plurality of transmission pairs, the transmission pair including the transmission tooth and the recess, is arranged in the circumferential direction.
2. The strain wave gear device according to claim 1 , wherein the number of the transmission pairs is 2×N or more and the transmission pairs are arranged at equal intervals in the circumferential direction.
3. The strain wave gear device according to claim 1 , wherein the plurality of transmission pairs includes:
a first pair with the transmission tooth positioned at one end in the circumferential direction of the recess when the cam rotates around the axis, and
a second pair with the transmission tooth positioned at the other end in the circumferential direction of the recess when the cam rotates around the axis.
4. The strain wave gear device according to claim 3 , wherein the number of the first pairs is N and the number of the second pairs is N.
5. The strain wave gear device according to claim 4 , wherein the first pairs and the second pairs alternately exist every 360°/(2×N) in angles centered on the axis.
6. The strain wave gear device according to claim 1 , wherein
in at least N pairs of the plurality of transmission pairs located at locations that correspond to the poles of the cam, the transmission tooth and the recess are separated in the radial direction, and
the first annular portion tolerates displacement of the second annular portion in the radial direction.
7. The strain wave gear device according to claim 1 , wherein
the first annular portion has a diameter smaller than that of the outer gear, and
the flex gear includes a connecting portion that connects the outer gear with the first annular portion and that is formed of the same material as the outer gear and the first annular portion and integrally formed with the outer gear and the first annular portion.
8. The strain wave gear device according to claim 1 , wherein the second annular portion is positioned radially inside of the first annular member.
9. The strain wave gear device according to claim 1 , wherein the second annular portion is positioned radially outside of the first annular portion.
10. The strain wave gear device according to claim 8 , further comprising:
a supporter that rotatably supports the outputter relative to the internal gear, wherein
the first annular portion and the second annular portion are positioned between the supporter and the cam,
the supporter includes an outer ring fixed to the internal gear with a screw that extends in the axial direction and an inner ring fixed to the outputter,
the internal gear includes:
an insertion hole that is formed along the axial direction and into which the screw is inserted; and
a specific portion positioned between the insertion hole and the first annular portion,
the specific portion includes an annular groove centered on the axis in a portion that faces against the outer ring in the axial direction, and
an O-ring fits into the annular groove.