SPEED REDUCER

PURPOSE:To enhance the speed reducing efficiency and prevent the generation of backlash as in the case of gear transmission by adopting a planetary roller system which is a speed reducing mechanism performed only by rolling friction transmission combined with a differential mechanism. CONSTITUTION:An input shaft, that is, a center roller 5, is rotated by the driving of a motor provided outside, so that a driven roller 6 in contact with the center roller rolls, as well as a supporting member, by which the rotary pivot of the driven roller is fixed, is integrally rotated in the same direction concentrically with the center roller. In other words, the input rotating speed is largely reduced by a planetary roller mechanism that the driven roller is rotated around the center roller while being rotated on its axis, and transmitted onto the output shaft side. A flange member 13 is contact with the driven roller is rotated in the same direction following the rotation of the driven roller, and an output shaft formed coaxially with the flange member is rotated. In this case, the assembling of a pressure ring 18, the driven roller and the flange member forms a differential mechanism by double rolling friction.