Worm wheels 1 and 2 are keyed to shafts 4 and 5, and rotate about fixed parallel axes E and F. Worm 3 is keyed to driving shaft 6 and rotates about fixed axis D. Worm 3 is built up of two parts, a and b. Part b extends over one-fourth of the worm circumference and has helical teeth. Part a extends over three-fourths of the worm circumference and has two annular teeth with zero lead angle. When driving worm 3 rotates continuously, worm wheels 1 and 2 rotate alternately with dwells. The rotation period of wheel 1 or 2 corresponds to the time it is in mesh with part b of worm 3. The idle period of wheel 1 or 2 corresponds to the period it is in mesh with the annular teeth of part a of the worm. Thus shafts 4 and 5 rotate alternately. When part a of the worm is in mesh with one of the worm wheels, the annular teeth of this part lock the worm wheel against unintentional rotation in its dwell period.
$2824$WG,D$