ROBOTIC WORK STATIONS FOR BENDING SHEET METALS COMPOSED OF A PRESS-BRAKE, AN ANTHROPOMORPHIC OR CYLINDRICAL OR CARTESIAN ROBOT, A SET OF GRIPPING MEMBERS, A CENTERING PLANE AND COMPLEMENTARY STOCKING MEMBERS FOR FINISHED AND SEMI-FINISHED PIECES WITH THE EXPRESS EXCLUSION OF INDUSTRIAL MACHINES FOR WORKING METALS BY ELECTRIC SPARK EROSION, BY ELECTRO-CHEMICAL PROCESSES BY ELECTRON BEAMS AND BY LASERS