There is a helical joint between the blue and beige gears. The violet compression spring tends to push the blue and beige gears apart from each other. Due to the helical joint, the blue gear turns when being pushed, thus eliminating the tooth backlash between the beige and yellow gears.
The second scene of the video shown how the backlash is eliminated under the violet spring action.
The last scene of the video shows the behavior of a spur gear drive without the eliminating backlash device. The rotation of the output gear (in beige) doesn’t correspond to the rotation of the input gear during the reversing process.
STEP files of this video:http://www.mediafire.com/file/1gcwtjvgjipahiv/EliminateBacklashGearSTEP.zip/file
Inventor files of this video:http://www.mediafire.com/file/pjpg085uwd9nf9d/EliminateBacklashGearInv.zip/file