Gears 1 and 2 rotate about fixed axes A and B. Gear 1 has one gear segment d, and gear 2 has two gear segments c. When driving gear 1 rotates continuously, driven gear 2 rotates only during the periods that segment d meshes with one of the segments c. To each revolution of gear 1, gear 2 turns through the angle ϕ=180°. Smooth, impactless operation when segments d and c come into engagement is due to the provision of transition cam surfaces a and k whose profiles are portions of the centrodes in the relative motion of gears 1 and 2. To prevent unintentional rotation of gear 2 and to lock it during its dwell periods, gear 1 has concentric locking surface b which engages concave surfaces 1 on gear 2.
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