Dual pinion anti-backlash carriage drive for a machine tool

Apparatus adapted for moving a carriage or slide along guide ways of a machine tool having an elongated rack, said apparatus comprising a frame, a pair of planetary gearboxes supported by said frame and having corresponding input and output shafts, a set of pinions mounted on said output shafts and positioned to engage the rack at longitudinally spaced locations, a reversible electric motor supported by said frame and having a motor shaft extending parallel to said input and output shafts, a set of pulleys having peripheryally spaced teeth and mounted on said motor shaft and said input shafts of said gearboxes ,an endless flexible and generally flat elongated timing belt having longitudinally spaced teeth and connecting said pulleys to provide for driving said pinions through said gearboxes in response to rotation of said motor shaft, a set of belt tension wheels having parallel spaced axes and positioned with said belt therebetween, a first slide member supporting said belt tension wheels for movement as a unit in a linear direction perpendicular to a plane defined by the axes of said input shafts, a second slide member supporting one of said belt tension wheels for movement relative to a second said belt tension wheel in the same said linear direction, and adjustable spring means for biasing said slide members and said belt tension wheels in said linear direction to produce a selected tension in said belt and a corresponding torque on each of said input shafts of said gearboxes for preloading said pinions against the rack.