Double-cycloidal-gear planetary speed reducer with adjustable reverse clearance error

The invention relates to a double-cycloidal-gear planetary speed reducer with an adjustable reverse clearance error. An eccentric mechanism with a thread contains a planetary shaft, a spline eccentric sleeve, an inner locking nut, a thread eccentric sleeve and an outer locking nut; a spline is arranged at one side of the planetary shaft; the spline is matched and connected with the spline eccentric sleeve; a thread is arranged at the other side of the planetary shaft and the other side of the planetary shaft is connected with the thread eccentric sleeve through the thread; the thread eccentric sleeve is positioned through the inner locking nut and the outer locking nut which are screwed on the thread of the planetary shaft; the spline eccentric sleeve and the thread eccentric sleeve are arranged in a non-180-degree symmetrical manner; two cycloidal gears are mounted on the spline eccentric sleeve and the thread eccentric sleeve respectively; the two cycloidal gears are non-symmetrically mounted, and the threa