Abstract: A counterforce cylinder and piston exert an upward force on the vertically movable slide of a machine. The cylinder pressure line handles reverse flows during operations of the slide. A pilot-operated checkvalve (normally closed) is inserted in the cylinder line between a pressure source and the counterforce cylinder, and is held open during usual operation of the machine. An accumulator is branch-connected to the cylinder line, at a point between the checkvalve and counterforce cylinder. During machine operations, the accumulator stores pressurized fluid; at shutdown of power, the fast-acting checkvalve closes and reliably seals the cylinder line while the accumulator provides pressure to maintain the counterforce cylinder and slide in a substantially constant holding position for several days.

Abstract: A spindle carrier, which is movable vertically by an electric servo motor through a relatively long ball screw, has a substantially constant counterbalance force maintained on it irrespective of whether it is moving up or down. This prevents compression or tension of the ball screw. The counterbalance force is maintained substantially constant through sensing the load on the spindle carrier and using the sensed load to vary the hydraulic pressure applied to a piston within a hydraulic cylinder and connected through a chain to the spindle carrier to apply the counterbalance force.