Abstract: In a wrist mechanism of the type that two sets of differential speed reduction devices are provided within a wrist and arranged symmetrically of and perpendicularly to the axis of an arm and that the adjustment of the angle of the wrist and the rotation of a tool are carried out through the differential speed reduction devices, a novel wrist mechanism is provided for preventing a wrist cover from entering into a dead point condition. The wrist mechanism comprises a guide protrusion and a guide. The guide protrusion is provided on the side of a bracket related by one of wrist covers on a wrist portion side, the side being located outside a speed reduction shaft and on the side of the wrist portion relative to the axis of an input shaft. The guide is provided on the inner face of the wrist cover at a point on a locus of the guide protrusion relative to the wrist cover, the point being defined by that at least the axes of a tool rotation shaft and input shafts coincide with each other.

Abstract: The present invention provides a wrist mechanism with three degrees of freedom for an industrial robot, which is compactly formed and to which a tool is mounted. The first degree of freedom is associated with a first input shaft for rotating a wrist portion at a low speed. The second and third degrees of freedom are associated with rotating the tool or tilting the wrist. In order to attain these motions, second and third input shafts concentrically arranged relative to the first input shaft are used for transmitting motion to, through bevel gears, speed reduction mechanisms each symmetrically disposed at right and left sides, and the outputs therefrom are used to drive the tool and wrist.