Backlash

Reduction gears are often used to couple the motor and load. Lost motion and dead zones can cause problems in this transmission mechanism. Lost motion is the displacement difference when positioning is done from one direction and from the reverse direction. This can cause a "dead zone" in which the motion is not transmitted from the motor to the driven side. Lost motion can arise from the shaft's torsional stiffness and friction, as well as when a physical gap exists in the transmission system. This gap is called backlash. Although zero backlash is preferable in theory, some backlash is necessary to prevent jamming.