Closed center valve control system

Claim 2

A fluid driven actuator system comprising: first piston means, said first piston means including a first drive piston disposed for motion in a cylinder; means coupling a first side of said first drive piston to a movable load; means for supplying pressurized fluid to said first piston means cylinder at the second side of said first drive piston; means for venting fluid from said first piston means cylinder at said second side of said first drive piston; a first normally deenergized and closed solenoid operated control valve for sealing said venting means, said first solenoid operated control valve opening said venting means to reduce the pressure in said first piston means cylinder when in the energized condition to thereby permit movement of said first drive piston in a first direction; modulator means responsive to a time varying signal having a mean value which is a function of load position error and to a threshold bias signal for generating a pulse width modulated valve control energization signal whenever said time varying signal exceeds said threshold bias signal whereby a dead zone for said piston means is created; and means for coupling valve control energization signals generated by said modulator means to the solenoid of said first control valve.

Claim 3

The apparatus of claim 1 wherein said means for supplying pressurized fluid comprises: a pressurized fluid source; and check valve means interposed between said fluid source and said first piston means cylinder to prevent reverse flow from said cylinder to said source, said check valve means cooperating with said first control valve to entrap operating fluid in said first piston means cylinder with said control valve in the normally closed condition.

Claim 4

The apparatus of claim 2 further comprising: shut-off valve means for disrupting communication between the pressurized fluid source and said check valve means whereby fluid may be entrapped in said piston means cylinder with the piston in any position.

Claim 5

A fluid driven actuator system comprising: first piston means, said first piston means including a first drive piston disposed for motion in a cylinder; means coupling a first side of said first drive piston to a movable load; second piston means, said second piston means including a second drive piston disposed for motion in a cylinder; means coupling a first side of said second drive piston to the movable load; means for supplying pressurized fluid to said first and second piston means cylinders at the second sides of said drive pistons; first control valve means for adjusting the pressure in said first piston means cylinder at the second side of said first drive piston to vary the position of said first drive piston; second control valve means for adjusting the pressure in said second piston means cylinder at said second side of said second drive piston to vary the position of said second drive piston; means for operating said first control valve means in response to valve control energization signals; means for operating said second control valve means in response to valve control energization signals; oscillator means for generating a time varying carrier signal; modulator means responsive to said time varying signal provided by said oscillator means and to signals commensurate with position errors of the movable load for generating a time varying signal having a mean value which is a function of load position error, said modulator means being further responsive to clockwise and counterclockwise threshold bias signals, said modulator means generating pulse width modulated valve control energization signals whenever said generated time varying signal exceeds one of said threshold bias signals whereby a dead zone for said piston means is created; means for coupling valve control energization signals generated by said modulator means and commensurate with position errors in a first direction to said first control valve operating means; and means for coupling valve control energization signals generated by said modulator means and commensurate with position errors in a second direction to said second control valve operating means.

Claim 6

A fluid driven actuator system comprising: first piston means, said first piston means including a first drive piston disposed for motion in a cylinder; means coupling a first side of said first drive piston to a movable load; second piston means, said second piston means including a second drive piston disposed for motion in a cylinder; means coupling a first side of said second drive piston to the movable load; means for supplying pressurized fluid to said first and second piston means cylinders at the second sides of said drive pistons; first control valve means for adjusting the pressure in said first piston means cylinder at the second side of said first drive piston to vary the position of said first drive piston; second control valve means for adjusting the pressure in said second piston means cylinder at said second side of said second drive piston to vary the position of said second drive piston; means for operating said first control valve means in response to valve control energization signals; means for operating said second control valve means in response to valve control energization signals; oscillator means for generating a time varying carrier signal; modulator means responsive to said time varying signal provided by said oscillator means and to signals commensurate with position errors of the movable load for generating a time varying signal having a mean value which is a function of load position error, said modulator means being further responsive to clockwise and counterclockwise threshold bias signals, said modulator means generating pulse width modulated valve control energization signals whenever said generated time varying signal exceeds one of said threshold bias signals whereby a dead zone for said piston means is created; means for coupling valve control energization signals generated by said modulator means and commensurate with position errors in a first direction to said first control valve operating means; and means for coupling valve control energization signals generated by said modulator means and commensurate with position errors in a second direction to said second control valve operating means.

Claim 7

The apparatus of claim 4 wherein said modulator means comprises: means responsive to signals commensurate with the actual and desired positions of the load for generating first and second error signals respectively commensurate with clockwise and counterclockwise position errors; first amplifier means connected to said oscillator means and said position error signal generating means and responsive to a signal commensurate with a clockwise position error and to said time varying carrier signal, said first amplifier means further being responsive to a clockwise threshold bias signal and generating a pulse width modulated valve energization signal for application to said first control valve means whenever the sum of said clockwise position error and time varying signals exceeds said clockwise threshold bias signal; and second amplifier means connected to said oscillator means and said position error signal generating means and responsive to a signal commensurate with counterclockwise load position error and to said time varying carrier signal, said second amplifier means further being responsive to a counterclockwise threshold bias signal and generating a pulse width modulated valve energization signal for application to said second control valve means whenever the sum of said counterclockwise position error and time varying signals exceeds said counterclockwise bias signal.

Claim 8

The apparatus of claim 4 wherein said control valve means each comprises: means for venting fluid from the associated piston means cylinder; and normally closed and deenergized solenoid operated valve means cooperating with said venting means to prevent escape of pressurized fluid from the associated piston means cylinder in the closed condition, energization of said valve means opening said venting means whereby a reduction in the associated cylinder pressure results.

Claim 9

the apparatus of claim 6 wherein said pressurized fluid supplying means comprises: a pressurized fluid source; conduit means for coupling said source to said first piston means cylinder, said conduit means including first check valve means for preventing reverse flow of fluid from said first piston means cylinder toward the source, said first check valve means cooperating with said first control valve means For entrapping operating fluid in said first piston means cylinder when said first control valve means is in the closed position; and second conduit means for coupling said source to said second piston means cylinder, said second conduit means including second check valve means for preventing reverse flow of fluid from said second piston means cylinder toward the source, said second check valve means cooperating with said second control valve means for entrapping operating fluid in said second means cylinder when said second control valve means is in the closed position.

Claim 10

The apparatus of claim 7 wherein said modulator means comprises: means responsive to signals commensurate with the actual and desired positions of the load for generating first and second error signals respectively commensurate with clockwise and counterclockwise position errors; first amplifier means connected to said oscillator means and said position error signal generating means and responsive to a signal commensurate with a clockwise position error and to said time varying carrier signal, said first amplifier means further being responsive to a clockwise threshold bias signal and generating a pulse width modulated valve energization signal for application to said first control valve means whenever the sum of said clockwise position error and time varying signals exceeds said clockwise threshold bias signal; and second amplifier means connected to said oscillator means and said position error signal generating means and responsive to a signal commensurate with counterclockwise load position error and to said time varying carrier signal, said second amplifier means further being responsive to a counterclockwise threshold bias signal and generating a pulse width modulated valve energization signal for application to said second control valve means whenever the sum of said counterclockwise position error and time varying signals exceeds said counterclockwise bias signal.

Claim 11

The apparatus of claim 8 further comprising: shut-off valve means for disrupting communication between said source and said check valve means and for venting said conduit means whereby fluid may be entrapped in said piston means cylinders with the piston in any position.

Claim 12

The apparatus of claim 9 wherein said shut-off valve means comprises: a solenoid controlled valve; and means responsive to a signal commensurate with load position error for generating control signals for said shut-off valve means solenoid controlled valve, said signal generating means establishing a dead band commensurate with the dead zone created by said modulating means.

Claim 13

The apparatus of claim 7 further comprising: shut-off valve means for disrupting communication between said source and said check valve means and for venting said conduit means whereby fluid may be entrapped in said piston means cylinders with the piston in any position.

Claim 14

The apparatus of claim 11 wherein said shut-off valve means comprises: a solenoid controlled valve; and means responsive to a signal commensurate with load position error for generating control signals for said shut-off valve means solenoid controlled valve, said signal generating means establishing a dead band commensurate with the dead zone created by said modulating means.

Claim 15

The apparatus of claim 3 wherein said shut-off valve means comprises: a solenoid controlled valve; and means responsive to a signal commensurate with load position error for generating control signals for said shut-off valve means solenoid controlled valve, said signal generating means establishing a dead band commensurate with the dead zone created by said modulating means.