Patent ID: 8549949

Claim:
A backlash adjustment mechanism comprising: a first cylindrical gear fixed in an axial position; a second cylindrical gear moveable along an axis thereof and meshed with the first cylindrical gear, and the second cylindrical gear defining a receiving hole extending substantially along the axis of the second cylindrical gear; and a helical-coil compression spring received in the receiving hole, abutting the second cylindrical gear, and biasing the second cylindrical gear towards the first cylindrical gear, wherein the helical-coil compression spring contacts with inner sidewalls of the receiving hole for limiting a radial movement of the helical-coil compression spring, addendum modification coefficients in the first and second cylindrical gears are linearly changed along their axes, respectively, an end of the first cylindrical gear with higher addendum modification coefficient meshes with an end of the second cylindrical gear with correspondingly lower addendum modification coefficient, and an end of the first cylindrical gear with lower addendum modification coefficient meshes with an end of the second cylindrical gear with correspondingly higher addendum modification coefficient.