Trunnion A of pinion 1 slides along fixed straight guide a. Composite gear 2 has circular slot b which does not extend around in a complete circle. Gear 2 rotates about fixed axis B. The teeth of gear 2 are located on both sides and at the ends of slot b, being made up of one internal and one external gear segments and two halves of an internal gear (at the slot ends). When pinion 1 rotates and axis A is in its lower position in guide a, pinion 1 meshes with the internal gear segment of gear 2 and gears 1 and 2 rotate in the same direction. When axis A is in its upper position in guide a, pinion 1 meshes with the external gear segment of gear 2 and gears 1 and 2 rotate in opposite directions. Thus gear 2 rotates alternately an incomplete revolution in each direction with dwells at the extreme positions. When pinion 1 meshes with the internal gear segment, gear 2 rotates at the angular velocity ω₂=ω₁(r₁/r₂), and when it meshes with the external gear segment, gear 2 rotates with the angular velocity ω₂'=ω₁(r₁/r₂'), where r₁ is the pitch radius of pinion 1, r₂ and r₂' are the pitch radii of the internal and external gear segments of gear 2, and ω₁ is the angular velocity of pinion 1.
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