Hydraulic positioning drive with pressure and position feedback control

• US 5,230,272 A
• Filed: 02/28/1991
• Issued: 07/27/1993
• Est. Priority Date: 06/29/1988
• Status: Expired due to Fees

• Current Assignee: Mannesmann Rexroth GmbH (Robert Bosch GmbH)
• Original Assignee: Mannesmann Rexroth GmbH (Robert Bosch GmbH)
• Inventors: Schmitz, Jurgen
• Primary Examiner(s): Look, Edward K.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/657,240
• Time in Patent Office: 880 Days
• Field of Search: 91/361, 91/459, 91/275, 91/367, 91/462, 91/433, 91/453, 91/363 R
• US Class Current: 91/361
• CPC Class Codes: G05B 19/39 using a combination of the means covered by at least two of the preceding groups G05B19/21, G05B19/27 and G05B19/33
• CPC Class Codes: G05B 2219/37357 Force, pressure, weight or deflection
• CPC Class Codes: G05B 2219/41301 Pilot valve, linear fluid control valve and power cylinder
• CPC Class Codes: G05B 2219/42123 Position loop then force, current loop

Abstract

A hydraulic drive is actuated by a CNC means via an electrically actuable valve. The pressure applied to the hydraulic drive or the force excerted by the hydraulic drive is supplied in the form of a signal to a pressure control means or a force control means. The output signal of the pressure- or force control means is supplied via a switch means--shortly prior to reaching the desired position value of the drive--to the electrically operated valve as a control signal. Simultaneously, the output signal of the switch means, which can be supplied to the valve, is interrupted, wherein the switching range shortly prior to reaching the desired position value is smaller than the admissible differential value, determined by the CNC means, i.e. the differential value between each actually present desired position value and actual value, or, wherein, with the switch-over from the position control to the pressure- and force control, respectively, the desired position value signal supplied by the CNC means is brought to the value of the actual position value. Thus, the invention provides the possibility to switch the position control circuit over to a force control circuit or a pressure control circuit and back, without having to take the risk of an automatic switch off or disconnection of the drive.

Claims

1. A hydraulic drive controllable by a valve which is electrically actuable comprising:

computerized numerical control means, receiving each actual position of the hydraulic drive as an actual value signal, for producing an output signal indicative of a difference between the actual position and a desired position,

pressure/force control means, receiving a signal representative of one of a pressure applied to the hydraulic drive or a force exerted by the hydraulic drive, and producing an output signal of said pressure/force control means,

switch means receiving said output signal of said pressure/force control means and said output signal of said computerized numerical control means, for supplying said output of said pressure/force control means shortly before reaching the desired position value of the drive to the electrically actuable valve as a control signal, and simultaneously therewith, interrupting the output signal, which can be supplied from the computerized numerical control means to the valve, whereby a switch over from control based on said output signal of said computerized numerical control means to control based on said output signal of said pressure/force control means of the desired position value signal supplied by the computerized numerical control means is brought to a value indicative of said actual position value.

2. The hydraulic drive controlled by a computerized numerical control control as set forth in claim 1 wherein the control means is in addition supplied with the output signal of said computerized numerical control means and is responsive to a change of the sign of the output signal (Sa) of the computerized numerical control means the control means is switched back due to a renewed switching of the switch means from the pressure control to the position control.

3. The hydraulic drive controlled by a CNC control as set forth in claim 1 wherein the switch over from the position control to the pressure control and force control, respectively, requires in addition a predetermined pressure increase and force increase, respectively.

4. The hydraulic drive controlled by a CNC control as set forth in claim 1, wherein the control means (14) reports the switch over from position control to to pressure control and force control, respectively, to the CNC control (6) by means of a signal.

5. 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.

6. 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.

7. The hydraulic drive controlled by a CNC control as set forth in claim 6 wherein the control means is additionally supplied with the output signal of the computerized numerical control means, and is responsive to a change of the sign of the output signal of the computerized numerical control means 1, wherein the control means is switched back due to a renewed switching of the switch means from the pressure control to the position control.

8. The hydraulic drive controlled by a CNC control as set forth in claim 6, wherein the switch over from the position control to the pressure control and force control, respectively, requires in addition a predetermined pressure increase and force increase, respectively.

9. The hydraulic drive controlled by a CNC control as set forth in claim 6, wherein the control means (14) reports to the control (6) by means of a signal the occurence of the switch over from the position control to the pressure control and force control, respectively,.

10. The positioning drive of claim 6 wherein the CNC control means (6) is connected with a position control means (7) which in turn is connected with the switching means (8), wherein the position control means (7) is further connected with the control means (14) so as to maintain the position control means (7) at a predetermined drift compensation when the pressure dependent switch-off of the CNC control means occurs, so that the switching operation from the pressure control mode to the position control mode is again available.