Composite gear 1 has teeth located on external a and internal b semicircular arcs, and rotates about fixed axis A. Pinion 2 rotates about fixed axis B. Pitch radii r₁,r₁' and r₂ of gears 1 and 2 comply with the condition r₁=3r₁'=3r₂. When gear 1 rotates constantly in one direction, driven pinion 2 rotates alternately in each direction. Angle ϕ₂‘ of clockwise rotation of pinion 2 is ϕ₂‘=3ϕ₁ and angle ϕ₂ of counterclockwise rotation of pinion 2 is ϕ₂=ϕ₁. To ensure continuous rotation of pinion 2 with only short stops at the extreme positions (at reversal), gear 1 is to be designed so that pinion 2 begins to mesh with internal teeth b at the instant it runs out of mesh with external teeth a. Impacts at the instant of engagement are avoided by the provision of supplementary conjugate cam surfaces having profiles with special curves.
$2317$SG,3L$