Hydraulic positioning drive with pressure and position feedback control

A computerized numerical controlled hydraulic positioning drive comprising:

• a hydraulic drive,
• a position transducer connected with said hydraulic drive to supply an actual value signal indicating an actual position of the hydraulic drive,
• a control valve, connected with said hydraulic drive to adjust said drive in accordance with an input signal,
• a computerized numerical control means connected with said position transducer for producing an output signal to control the control valve,
• a pressure control means for producing an output signal which controls the control valve,
• a switching means for applying to the control valve either the output signal of the computerized numerical control means or the output signal of the pressure control means depending on a state of said switching means, and
• control means for controlling switching of the switch means into either a position control mode or a pressure control mode, the control means receiving information about pressure conditions in the hydraulic drive and switching the switching means responsive to information indicating that a predetermined pressure has been reached, the control means simultaneously controlling the pressure controller to initiate its predetermined control operation, and simultaneously controlling the computerized numerical control means to stop position control operation presently under way and to supply a differential control signal "zero", thus avoiding an automatic shut-off of the computerized numerical control control means.

A controlled hydraulic drive comprising:

• a computerized numerical control means, receiving each actual position of the drive as an actual value signal;
• for producing an output controlling signal based on said actual position and a desired position;
• pressure control means, receiving a signal indicative of a pressure of the hydraulic drive, for producing a pressure output signal based thereon;
• an electrically actuable valve operative to actuate said hydraulic drive;
• a switch having inputs receiving said output controlling signal and said pressure output signal, and an output connected to said electrically actuable valve;
• and
• control means for controlling said switch means to actuate it between a first position connecting the computerized numerical control means to said valve and a second position connecting said pressure control means to said valve, said control means commanding said pressure output signal of said pressure control means to be supplied to the electrically actuable valve as a control signal via said switch means at a position shortly before reaching the desired position of the drive, while simultaneously interrupting the output signal of the computerized numerical control means supplied to the valve by the switch means, and wherein said position shortly before reaching the desired position is smaller than an admissible differential value between each desired position value and said actual value.