Control arrangement with a pulse-length modulator for a piston

Claim 2

An hydraulic servo system, comprising a positionable member movable in a first direction and alternatively in an opposite second direction; means for selecting a desired position for said member; means for determining the actual position of said member; and electrohydraulic control means operative when the difference between the actual and desired positions is greater than a predetermined value for effecting rapid movement of said member in a single one of said directions towards the desired position, and operative when said difference is reduced to less than said value for causing said member to perform an oscillatory movement composed of longer motions in direction towards the desired position alternating with shorter motions in opposite direction so as to effect a net slower movement of said member to the desired position.

Claim 3

A system as defined in claim 1, wherein said member is a hydraulic piston movable in a hydraulic cylinder, and wherein said control means includes a source of pressurized fluid, conduit meaNs for connecting said source of fluid and the interior of said cylinder, electrically actuated first valve means operative when actuated for so controlling the flow of fluid from said source to the interior of said cylinder as to effect rapid movement of said piston in one or the other of said directions, electrically actuated second valve means operative when actuated for so controlling the flow of fluid from said source to the interior of said cylinder as to cause said piston to perform said oscillatory movement, and valve-actuating means for causing said first valve means to effect rapid movement of said piston towards the desired position when said difference exceeds said value, and for causing said second valve means to cause said piston to perform said oscillatory movement when said difference is reduced to less than said value.

Claim 4

A system as defined in claim 2, wherein said valve-actuating means includes pulse-length-modulating means for generating a train of pulse-length-modulated pulses, the ratio of the duration of the pulses to the time interval between successive pulses varying as a function of said difference when said difference is less than said value, and wherein said valve-actuating means comprises means for so controlling said second valve means as to cause said piston to move in one of said directions during each of said pulses and in the opposite direction during the time intervals between successive pulses, so as to cause said piston to perform said oscillatory movement.

Claim 5

A system as defined in claim 3, wherein as said difference approaches zero said ratio approaches a value causing said piston to oscillate about the desired position in the steady state.

Claim 6

A system as defined in claim 2, wherein said valve-actuating means includes pulse-length-modulating means for generating a train of pulse-length-modulated pulses when said difference is less than said value, the ratio of the duration of the pulses to the time interval between successive pulses varying as a function of said difference when said difference is less than said value, and wherein said valve-actuating means comprises means operative only when said difference is less than zero for so controlling said second valve means as to cause said piston to move in one of said directions during each of said pulses and in the opposite direction during the time intervals between successive pulses, so as to cause said piston to perform said oscillatory movement.

Claim 7

A system as defined in claim 5, wherein as said difference approaches zero said ratio approaches a value causing said piston to oscillate about the desired position in the steady state.

Claim 8

A system as defined in claim 4, wherein said valve-actuating means is operative for causing said first valve means to effect said rapid movement of said piston towards the desired position only when said difference exceeds said value.

Claim 9

A system as defined in claim 2; and further comprising pressure-regulating valve means for regulating the pressure at which said fluid leaves said source.

Claim 10

A system as defined in claim 1, wherein said member is a hydraulic piston movable in a hydraulic cylinder and dividing the cylinder into two separate chambers located at axially opposite sides of said piston, and wherein said control means includes a source of pressurized fluid, a collection tank for fluid, a conduit connecting said source to one of said chambers, a further conduit connecting said source to the other of said chambers, an additional conduit connecting said other of said chambers to said tank, a first shunting conduit shunting said further conduit, a second shunting conduit shunting said additional conduit, first valve means comprising a pair of electrically actuated first valves, one disposed in said further conduit and the other disposed in said additional conduit, and operative when one or the other is actuated for effecting movement of said piston in one or the other of said directions, electrically actuated second valve mEans connected to said first shunting conduit and connected to said second shunting conduit for alternatively blocking flow through one or the other of said shunting conduits and operative when unblocking said first shunting conduit for effecting movement of said piston in one direction and operative when unblocking said second shunting conduit for effecting movement of said piston in the opposite direction, and valve actuating means operative when said difference exceeds said value for actuating the respective one of said first valves to effect said rapid movement of said piston towards the desired position, and operative when said difference is reduced to less than said value for actuating said second valve means to unblock said first and second shunting conduits alternately to cause said piston to effect said oscillatory movement.

Claim 11

A system as defined in claim 9; and further including a pair of pressure-regulating valves, one disposed in said first shunting conduit and the other disposed in said second shunting conduit.

Claim 12

A system as defined in claim 9, wherein said piston includes a piston rod mounted for sliding movement through an opening in the wall of said cylinder and wherein said rod extends through said one chamber.

Claim 13

A system as defined in claim 11, wherein said piston rod has a cross-sectional area substantially equal to the effective cross-sectional area of the respective axial end face of said piston.

Claim 14

A system as defined in claim 3, wherein said pulse-length-modulating means comprises an operational amplifier having an inverting and a non-inverting input, means for maintaining one of said inputs at a constant potential, a pair of input resistors each connected at one end to the other input of said amplifier, the other end of one of said input resistors being connected to said means for selecting a position for said member, and the other end of the other of said input resistors being connected to said means for determining the actual position of said member, an adjustable capacitor connected between ground and said other of said inputs of said amplifier, and adjustable feedback resistor connecting the output of said operational amplifier to said other input thereof, and a coupling resistor connecting the output of said operational amplifier to said one input thereof.

Claim 15

A system as defined in claim 7, wherein said valve-actuating means includes three-point regulator means comprising an operational amplifier having in its input circuit a diode-resistor network for determining the algebraic sign of said difference and whether said difference is less than said value.

Claim 16

A system as defined in claim 14, wherein said regulator means has an input to which is applied the sum of an electrical signal proportional to the position of said member, an electrical signal proportional to the rate of movement of said member and an electrical signal proportional to the desired position of said member.

Claim 17

A system as defined in claim 15, wherein said input of said regulator means has an input resistor connected to said means for determining the actual position of said member, and also a differentiating capacitor connected in parallel with said input resistor.