Hydraulic-frictional system for rotating the arm of a forging manipulator

A hydraulic-frictional system for operating a forging manipulator, comprising:

• a forging-manipulator arm journaled for rotation about a horizontal axis and carrying tongs engageable with a workpiece;
• first and second clamps surrounding said arm and each having a pair of clamping jaws adapted to embrace said arm upon displacement of the jaws of each clamp toward one another and to allow free rotation of said arm relative to the respective clamps in a spread-apart position of the jaws thereof, each pair of jaws being pivotally connected at one end and being provided at its other end with a respective double-acting hydraulic clamping cylinder adapted to displace the jaws of each pair toward and away from one another;
• respective double-acting power cylinders each pivotally connected to a separate one of said clamps, said power cylinders having a head chamber and a rod chamber;
• conduit means hydraulically connecting pressurizable compartments of said clamping cylinders for inverse operation whereby one of said clamps seizes said arm while the other of said clamps permits free rotation thereof;
• and
• means for alternately pressurizing one of said head or rod chambers of said power cylinders to rotate said first and second clamps, said one clamp seizing said arm and thereby displacing it while the other of said clamps being rotated without affecting rotation of said arm.