Pin wheel 1 with pin a rotates about fixed axis A and meshes with slots d of rack 2 which slides along fixed guides b-b. The working surfaces of slots d are straight. Wheel 1 has concentric locking lug b and rack 2 has concave locking surfaces e. When driving pin wheel 1 rotates continuously at uniform velocity, driven rack 2 travels intermittently with dwells at nonuniform velocity according to a sine-curve law. During the dwells, concentric lug b engages the corresponding concave surface e, preventing unintentional motion of rack 2.
$2607$PG,D$