A new traction drive mechanism, which delivers power from its input shaft to its output shaft using friction produced by the elastic ring, was designed and manufactured with the glass fiber epoxy composite material. The traction drive can have higher speed reduction ratio with simple structure than conventional friction drives. In addition it has good characteristics such as smooth power transmission, no backlash, and high torsional stiffness, although it has a smaller torque transmission capability compared to other toothed mechanisms because the torque transmission capability of the traction drive is limited by its frictional torque.
The major speed reduction of the traction drive is originated from the circumferential difference between the flexspline and the elastic ring, which is 1~10 % of the circumference of the elastic ring. Then the speed reduction of the flexspline is 10~100 times.
The flexspline in the traction drive should not only be flexible in the radial direction to produce the friction between its surface and the surface of the elastic ring when it is pushed onto the elastic ring by the inner rollers, but also be stiff in the torsional direction to deliver accurate angular motion. Since the conventional isotropic materials such as the steel and the aluminum cannot meet these stiffness requirements simultaneously, the glass fiber epoxy composite material was adopted to directionally tailor the stiffnesses.
To eliminate wear of the composite flexspline, a thin ring of the same axial length of the elastic ring was manufactured with the high strength steel and adhesively bonded to the flexspline.
The stress of the composite flexspline was calculated by finite element method and the assembled traction drive was statically and dynamically tested in order to assess the vibration and fatigue characteristics.
