Single-tooth driving wheel 1 rotates about fixed axis A. Rack 2 slides along fixed guides f-f. When wheel 1 rotates, its tooth d consecutively engages teeth e of rack 2, imparting intermittent sliding motion to the rack. During dwells of rack 2, concentric locking surface a of wheel 1 engages a concave surface b of rack 2, locking the latter against unintentional translatory motion.
$2354$SG,D$