Patent ID: 7900890

Claim:
A worm-rack type transmission device comprising: a linear rack, an outer surface of which has a large number of rack teeth at predetermined pitch intervals; a worm wheel having a frustocone-shaped body, an outer surface of which has a series of a toothed streak helically running therealong in registry with said rack teeth from a minimum diameter portion to a maximum diameter portion of said frustocone-shaped body at the same pitch intervals as said linear rack has; a curved side portion provided on a side surface of each of said rack teeth to be in registry with said toothed streak to have a recess profiled by a part of an ellipsoidal surface along a face-width direction of said rack teeth with a major diameter of said ellipsoidal surface in parallel with said rack teeth, said major diameter being a radius of curvature equal to that of any portion of said toothed streak residing from said minimum diameter portion to said maximum diameter portion, said curved side portion being twisted against said face-width along a torsional direction of said toothed streak corresponding to a changing rate of a torsional manner of said toothed streak; said worm wheel being placed on said linear rack with said worm wheel inclined to form a predetermined angle against said linear rack, so as to bring said toothed streak into engagement with said curved side portion, so that said worm wheel transmits its rotational movement to said linear rack to convert said rotational movement into a linear movement upon rotationally driving said worm wheel.