Pin rack 1 with pins a slides along fixed guide f-f and meshes with teeth d of sprocket 2 which rotates about fixed axis A. The profiles of teeth of sprocket 2 are involutes of a circle. Rack 1 as flat locking surfaces e and sprocket 2 has flat locking surfaces b. When driving rack 1 travels at uniform velocity, driven sprocket 2 rotates at uniform velocity with dwells. Unintentional rotation of sprocket 2 is prevented during dwells by the engagement of a flat surface e and the corresponding flat surface b of the sprocket.
$2608$PG,D$