Industrial robot equipped with articulated arm unit

Claim 1

In an industrial robot equipped with an articulated arm unit including a first arm pivotally attached at its basal end portion to a shoulder shaft, a second arm pivotally coupled at its basal end portion to the free end of the first arm by means of an elbow shaft, a holder case pivotally connected to the free end of the second arm by means of a wrist shaft, and a holder supported by the holder case in such a way that the holder is turnable about an axis, which extends perpendicularly to the wrist shaft, by means of a shaft journalled on the wrist shaft, wherein the improvement comprises: a first shaft and a second shaft disposed on the same axis and rotatable independently from each other to thereby form the shoulder shaft for the first arm; a differential transmission mechanism comprising a floating shaft extending perpendicularly to the second shaft and journalled on the second shaft, a pair of small bevel gears journalled on the floating shaft with the floating shaft interposed therebetween, a pair of large bevel gears journalled on the floating shaft respectively at locations adjacent to both free ends of the floating shaft, a pair of small bevel gears provided respectively on the first shaft and the second shaft in a face-to-face relationship and with the first mentioned pair of small bevel gears interposed therebetween so as to form an inner bevel gear unit, and a pair of large bevel gears provided respectively on the first shaft and the second shaft in a face-to-face relationship and with the first mentioned pair of large bevel gears interposed therebetween so as to form an outer bevel gear unit, said differential transmission mechanism arranged over mutually-opposing end portions of the first and the second shafts; and a first drive means formed by the first shaft and a first coupling means comprising a combination of a pair of sprockets and endless chain extending therebetween and being connected thereto for rotating the holder, and a second drive means formed by the second shaft and a second coupling means comprising a combination of a pair of sprockets and another endless chain extending therebetween, and being connected thereto for rotating the holder case as well as by a third coupling means connected to the differential transmission mechanism so as to compensatively rotate the holder.