Circumferential spatial tooth profile modification of flexspline for strain wave gear (A novel method and a case study)

Strain wave gear, also known as "harmonic drive" is widely used in the industrial robotics field due to the excellent deceleration performance. The tooth modification of the flexspline faces the requirements of high accuracy and service life. In this paper, a novel spatial tooth profile modification method along the circumferential direction of flexspline for strain wave gear is proposed. The circumferential modification method has a small change of meshing point position and working pressure angle, which is beneficial to maintain the transmission accuracy and improve the service life. In addition, the relation model of spatial motion between hob and flexspline, and the relation between tooth profile and modification quantity are study in the view of engineering application aim to reveal that the principle of circumferential modification is the rotation of the tooth profile along the center of the tooth apex circle. And the feasibility of circumferential modification is verified by a actual machining. Then, two main factors, circumferential modification quantity and radius of flexspline indexing circle are analyzed. Afterward, the novel stepwise modification of the circumferential spatial tooth profile of flexspline is introduced. Finally, a case study of circumferential spatial tooth profile modification of flexspline for strain wave gear is conducted. The case study shows that the maximum distance offset value in circumferential modification is 7.8 mu m, which is smaller than the traditional modification value (13.2 mu m), and the maximum working pressure angle value is 2.24 degrees, which is smaller than the minimum value (3.93 degrees) in traditional modification. And the FEM results and the cross-section tooth pairs comparing with the theoretical model also show the possibility of the proposed modification method.