Two-tooth driving gear 1 turns about fixed axis A. Toothed racks 2 and 3 slide along fixed guides b and a. When gear 1 oscillates, racks 3 and 2 slide in opposite directions with dwells. Concentric locking surface e on gear 1 engages concave surfaces d on the racks, locking the latter against unintentional motion during their dwells.
$2356$SG,D$