Abstract: A pneumatically powered valve actuator is disclosed including a valve actuator housing, a main piston reciprocable within the housing along an axis and a pair of auxiliary pistons fixed to and movable with the main piston. The main piston has a pair of oppositely facing primary working surfaces. A pair of air control valves reciprocable along said axis relative to both the housing and the main piston between open and closed positions control air flow from a pressurized source causing the main piston and the pair of auxiliary pistons to move. Each auxiliary piston forms, in conjunction with a surface of the corresponding air control valve, a variable volume annular chamber. The variable volume chamber function during the early portion of piston movement to apply a reclosing force to the air control valve and during a latter portion of the piston movement to vent air compressed by the piston during damping. This venting of the residual air is in an axial rather than a radial direction.

Abstract: A fast acting valve actuator for actuating an intake or exhaust valve in an internal combustion engine of a type which is hydraulically powered and command triggered is disclosed and includes a cylinder with a power piston having a pair of opposed working surfaces or faces reciprocable within the cylinder along an axis between first and second extreme positions. A cylindrical control valve is located radially intermediate the reservoir and the cylinder, and is movable upon command to alternately supply high pressure fluid from a reservoir of high pressure hydraulic fluid to one face and then the other face of the power piston causing the piston to move from one extreme position to the other extreme position. The cylindrical control valve may be a shuttle valve which is reciprocable along the axis of the power piston between extreme positions with control valve motion along the axis in one direction being effective to supply high pressure fluid to move the piston in the opposite direction.

Abstract: For detecting the pressures occurring at a control valve pressure pickup cells are provided and for processing the pressure measuring signals evaluating electronics are provided which together with the pressure pickup cells is arranged on an intermediate plate associated with the control valve. With this arrangement signals may be formed which monitor and control the mode of operation of the consumer governed by the control valve. By arranging the components necessary for the control circuit on the intermediate plate a standardized design is made possible in which the constructional expenditure is greatly reduced.

Abstract: A bistable electronically controlled pneumatically powered transducer for use, for example, as a valve mechanism actuator in an internal combustion engine is disclosed. The transducer has a piston which is coupled to an engine valve, for example. The pistion is powered by a pneumatic source and is held in each of its extreme positions by pneumatic pressure under the control of control valves which are in turn held in their closed positions by pressurized air and/or permanent magnet latching arrangements and are released therefrom to supply air to the piston to be pneumatically driven to the other extreme position by an electromagnetic neutralization of the permanent magnet field. A pair of auxiliary pistons movable with the piston compress air to a pressure above the pressure of the pneumatic source for aiding reclosure of the control valves as well as aiding maintenance of those control valves in their closed positions thereby reducing the size and cost of the latching permanent magnets.

Abstract: A relay valve unit having a control pressure communication line for the relay valve equipped with a reducer unit so that when activating the relay valve, any delay is either non-existent or negligibly larger than would be required for the complete opening of the relay valve.

Abstract: A novel digital servo valve system for use in displacing an actuator is capable of operating either in closed or open loop mode. The system includes a controller that compares computed values of actuator parameters with preselected parameter values and iteratively determines therefrom command signals for the servo valve. The servo valve is characterized by a ball screw mechanism that eliminates mechanical backlash and a torsion bar which increases radial and angular compliance. A servo valve provided according to the present invention also displays reduced flow forces using a simple, inexpensive valve body in combination with a uniquely configured displaceable spool.

Abstract: A duty ratio for operating a solenoid is determined by calculating a duty ratio in each of basic periods and determining an operational time for which the solenoid is to be operated within each of the basic periods, based on the calculated duty ratio. When the duty ratio is reduced to the extent that the operational time is shorter than a minimum possible time of operation of the solenoid, an operational time for which the solenoid is to be operated is determined within a new period composed of a plurality of consecutive basic periods.

Abstract: A hydraulic control method which includes a step of changing the time rate of introduction per a predetermined unit time of pressurized oil into an oil passage connected to a hydraulically-operated load device, such as a clutch of an automatic transmission, from a first time rate to a second time rate, thereby changing the time-based average oil pressure inside the oil passage from a first oil pressure value to a second oil pressure value. The time rate of introduction of the pressurized oil into the oil passage is changed from the first time rate to the second time rate via a third pressurized oil introduction time rate corresponding to a third oil pressure value different from the first and second oil pressure values. If the second oil pressure value is greater than the first oil pressure value, the third pressurized oil introduction time rate is substantially 100%. If the second pressure value is smaller than the first, the third time rate is substantially 0%.

Abstract: A bistable electronically controlled pneumatically powered transducer for use, for example, as a valve mechanism actuator in an internal combustion engine is disclosed. The transducer has a piston which is coupled to an engine valve, for example. The piston is powered by a pneumatic source and is held in each of its extreme positions, and air control valves are held in their closed positions by pressurized air and/or permanent magnet latching arrangements and the control valves are released therefrom to supply air to the piston, and the piston is released therefrom to be pneumatically driven to the other extreme position by an electromagnetic neutralization of the permanent magnet field. The piston forms a part of the magnetic latching circuit and that magnetic circuit also includes a radially slotted ferromagnetic member to both complete the magnetic circuit and provide a good air communication path from a high pressure air inlet to the control valve.

Abstract: The invention concerns a valve structure comprising a valve body, a chamber space disposed within the valve body, two running spindles and seats disposed to cooperate and placed within the chamber space, each running spindle enabling the aperture in the respective seat to be controlled. The valve structure comprises an input duct, a return duct and a working duct, the ducts being connected to the chamber space, a pressurized fluid being supplied through the input duct in the chamber space and the fluid being conducted through the controllable apertures with the aid of the running spindles either through the return duct out from the valve means to a tank or equivalent, or through the working duct to at least one power cylinder or equivalent, and the position of the running spindles and the size of the apertures being controlled with the aid of pilot valves.

Abstract: A neutral position resetting device for a servo actuator is described, having reset means that is actuated when the control of the servo actuator by actuator valve means becomes inoperative. The reset means ordinarily separated from a spool of the actuator valve means resets the servo actuator to a neutral position by applying a driving force and forcibly moving the spool.

Abstract: A fluid apparatus includes a pneumatic cylinder having a main body, a piston, and a hollow rod. A ball screw shaft engaged with a ball nut fixed to the piston is rotatably and axially unmovably mounted in the cylinder and extends in the hollow rod. A magnetic brake for braking the ball screw shaft is fixed to an end portion of the main body of the cylinder. The number of revolutions of the ball screw shaft is detected and outputted in a signal form by a rotary encoder. A primary solenoid controlled valve reciprocates the piston by connecting a pressure source either to a first or second port of the cyliner, and secondary solenoid controlled valves connect a pressure source either to a first braking pressure port or to a second braking pressure port.

Abstract: A pneumatically powered valve actuator is disclosed and includes a valve actuator housing, a working cylinder within the housing having a pair of opposed contoured end faces, and a main piston reciprocable within the cylinder along an axis. The main piston has a pair of oppositely facing primary working surfaces contoured substantially the same as the opposed end faces of the working cylinder to mate therewith providing a small minimum volume and, therefor, a high compression ratio. A pair of air control valves are reciprocable along the axis relative to both the housing and the main piston between open and closed positions for selectively supplying high pressure air to the piston primary working surfaces. The contoured end faces each include a central opening, an outer annular flat surface, and an intermediate frustoconical surface connecting the central opening and the flat surface.

Abstract: A time division multiplexed (TDM) hydraulic control system having a plurality of channels, each channel having a servo actuator. Electrical demand signals are arranged in TDM sequence and applied to a pilot valve so that the pilot valve produces a plurality of hydraulic signals. The hydraulic signals in turn are coupled to a separate commutator which distributes the hydraulic signals to the associated channels. The pilot valve is arranged with a full annular output port to maximize the port area and thereby the flow rate to the channels. The commutator size and port area is coordinated to that of the pilot valve to minimize pressure drop across the commutator and to maximize flow rate to the channels.

Abstract: A pre-set fluid actuator for setting the roll gap of a rolling mill having a transducer for detecting actuator movement and an electrohydraulic servovalve for controlling its position, a control system for compensating for the compressibility of the actuator fluid caused by the rolling force in a manner that requires no operation of the servovalve by creating a pre-set anticipating compression compensation signal and reducing the output of this signal by the output of a signal representing the actual fluid compression caused by the actual rolling force.

Abstract: In a fluid control valve, a check valve is provided between the pump port and the first fluid chamber and allows the fluid to pass therethrough only in a direction from the pump port to the first fluid chamber, a down control valve is provided between the first fluid chamber and the second fluid chamber, an up control valve is provided between the first fluid chamber and the third fluid chamber, the fluid is allowed to flow from the pump port to the cylinder port through the check valve and through the down control valve when they are opened, and the fluid from the cylinder port to the tank port is allowed to flow through the down control valve, through the first fluid chamber and through the up control valve when they are opened. The fluid control valve can be obtained simple in structure and high in precision, and be allowed a reduction in cavitation and noise.

Abstract: A system for the control of a fluid flow control valve which controls the supply of fluid to an actuator to control the movement of a component such as a tractor implement hitch in response to a selected operating parameter such as hitch position or draft force. The system enables the desired value of the selected parameter to be set and this desired value is compared with the actual sensed value of the parameter to provide a parameter error signal. A start-up control function is provided to improve the initial speed of response of the system. The start-up control function is arranged on each detection of a parameter error signal to apply a start-up signal to the valve to initiate movement of the component and, if no movement results, to increase the start-up signal until movement of the component is detected whereupon the increase in the start-up signal is stopped and the magnitude of the signal applied to the valve is dependent on the parameter error signal so as to tend to reduce the error signal to zero.

Abstract: An electropneumatic rotary actuator has proportional fluid valving providing introduction and exhaust of pressurized fluid to and from a working chamber of the actuator. By control of the admission angle and venting angle of the fluid pressure and flow with respect to top dead center and bottom dead center of a working piston of the actuator both the torque level and gas consumption rates of the actuator may be controlled. Further by modulating the average working fluid pressure within the actuator the stiffness or resistance to backdriving of the actuator may be controlled. A proportional linear electrical solenoid is disclosed and employed in the actuator of the present invention to drive a double-acting closed-centered valve device. Because of its lightweight, relatively simplicity, high stiffness to backdriving, and relatively low gas consumption rate, the present actuator is expected to find application in airborne vehicles.

Abstract: A solenoid-controlled valve arrangement is provided which includes a relay valve having in its control line a series arrangement of a shut-off valve and a shifting valve. Each of the shut-off valve and the shifting valve is solenoid-controlled.

Abstract: A novel electro-hydraulic control system for use with a helicopter includes a plurality of electro-hydraulic modules which provide control signals to corresponding blade actuators. A controller receives helicopter parameter input signals as well as pilot command signals and generates the control signals in accordance with preestablished algorithms. The system is characterized by a hydraulic slip ring that transmits the hydraulic control signals from the fuselage to the rotating assembly. Consequently, the present system provides "fly by wire" operation with individually addressable helicopter blades.

Abstract: In a pneumatic actuator wherein air pressure in a diaphragm compartment (38) is changed by controlling solenoid valves (39, 39 and 41) thereby to output a displacement; an intake solenoid valve (39) has a spring (30h) which penetrates a center part of a fixed iron core (39e) and urges a movable iron core (39f), and the solenoid valves (39, 39 and 41) are mounted on a housing (31) in a triangular disposition with terminal side thereof faced to the housing (31), and besides, one of terminals of each solenoid valve (39 or 41) is secured with each other at a center part of the triangular disposition, and the other terminals are disposed outward of the triangular disposition.

Abstract: A hydraulic operating apparatus for a circuit interrupter comprises a conversion unit for converting input information from the exterior concerning a speed control pattern into an electrical signal for driving a linear or servo motor according to the closing and interrupting commands, the motor drive signal provided from the converting means being transmitted to the motor such that the displacement of the motor causes the hydraulic control valve apparatus to be operated to switch the fluid passages to selectively drive the hydraulic cylinder in different directions, and that the position during the switching of the hydraulic control valve driven by the motor is made different from the final stop position at its interruption or closed state to provide a throttle effect of a throttle in the hydraulic control valve thereby controlling the speed of the hydraulic cylinder.

Abstract: A hydrostatic drive assembly with an adjustable pump driven by a primary power source, which acts on several consumers of hydrostatic energy, is disclosed which has a control and regulating device with nominal speed value pickups and adjustable restrictors for each consumer. In order to obtain a control and regulating device at a low production cost, one that operates with a low power loss, it is proposed that the nominal speed value pickup send an electric signal to an electronic control device, that each consumer be provided with an actual speed value pickup, which the control device, and the restrictors assigned to each of the consumers in their connection lines are designed as electromagnetic throttle valves controlled by the electronic control device.

Abstract: A drive control system, which is suitable for use in a hydraulic machine, is equipped with an electric lever device having a manipulation lever and a potentiometer for generating an electrical manipulation signal corresponding to the degree of each manipulation of the lever, a control valve connected to a hydraulic circuit adapted to actuate a hydraulic actuator, and a controller unit equipped with a main controller for receiving the manipulation signal and computing a control signal for the control valve on the basis of the manipulation signal and an output device for generating an electrical actuation signal corresponding to the control signal.

Abstract: Means for servo-controlling the position of a pneumatic actuator (14) comprise a circuit (20) for controlling a valve (10) for feeding the actuator, and a position sensor (30) and an acceleration sensor (34) which are associated with the moving member (16) of the actuator and which provide position and acceleration signals to the control circuit (20). The invention improves the stability and the accuracy with which the position of a pneumatic actuator is servo-controlled.

Abstract: An electronic pneumatic limb control system for a pneumatically actuated flexible limb is disclosed. The system includes a computer for providing signal data corresponding to a plurality of successive events of air introduction and non-air introduction, respectively, into the flexible limb during a predetermined limb movement. The computer signal data provides for time-varying the air introduction to the non-air introduction for the successive events thereof during the limb movement so as to minimize oscillation and overshoot. The system also provides for successive events of air exhaustion and non-air exhaustion to return the limb to a position of rest after the predetermined limb movement.

Abstract: A control system for a two way acting hydraulic servomotor wherein the servomotor is connected in the diagonal of a bridge circuit that includes four magnetic valves with a pair of the valves being normally open in a non-energized condition being connected to the one end of the servomotor and to the container and a second pair of the valves being normally closed in a deenergized condition being connected to the opposite end of the servomotor and to a pressure source. Circuitry provides pulse trains that are modulatable to control the operation of the magnetic valves and thereby the application of pressurized fluid to the opposite ends of the servomotor.

Abstract: In a motor vehicle such as a truck or the like having a battery-operated low voltage electrical system, an hydraulically powered system for operating one or more high power hydraulic rams or the like and a pneumatic system for regulating the operation of the hydraulic system, the improvement wherein the pneumatic system is powered by a low capacity compressor which is powered by a low voltage electric motor which is electrically connected to the low voltage circuit of the motor vehicle to drive the compressor to pressurize the pneumatic system as required in use.

Abstract: A pneumatic constant-velocity running apparatus employing a diaphragm type actuator in which a portion or the whole of a control circuit for the actuator is made of a hybrid IC and the hybrid IC portion with a protector is fixedly mounted onto the outer surface of an housing of the actuator. The apparatus is made compact and further be remarkably improved in an operation accuracy and in noise-proof property as well as in heat radiating property.

Abstract: For setting and guiding a band running round two rolls the bearings of the roll on either side are each adjustable by a hydraulic or lifting cylinder. Each hydraulic cylinder comprises a position control circuit. The position desired value applied jointly to the position control circuits is varied by a tension-dependent control in such a manner that in the position adjustment a maximum admissible tension force is not exceeded. Furthermore, the position desired value has superimposed thereon a correction control by which the center setting of the band is monitored. The arrangement is preferably provided for positioning and tension-dependent adjustment of the encircling metal band of a sheet casting apparatus.

Abstract: According to the parent patent on inadequate power of the delivery pump the flow rate set at the directional control valves for the consumers is reduced in equal proportions in that electrical signals proportional to the flow rates are supplied to a summation stage and the sum voltage is compared in a comparison stage with a limit value corresponding to the maximum pump delivery flow. When the limit value is exceeded a control signal is generated with which the stroke of all the driven directional control valves can be jointly reduced. According to the application of addition the signal voltage supplied to the summation stages and corresponding to the respective flow rate can be obtained in a displacement pickup associated with each directional control valve or in a pressure pickup measuring the pilot pressure if the directional control valves are not controlled electrically but hydraulically.

Abstract: Agricultural vehicles have heretofore lacked an adaptive implement hitch control and have correspondingly suffered from poor controllability of the hitch when the mass of the implement is varied significantly. The apparatus employs a sensor connected to and movable with the hitch such that a variable magnitude electrical signal is delivered which corresponds to the instantaneous hitch position. This signal is electronically differentiated to produce a signal indicative of actual hitch velocity. The hitch position and velocity signals are both used as feedback signals to close the control loop of the control and thereby provide an adaptive hitch velocity control.

Abstract: A device for converting energy of a fluid medium into mechanical work comprises a hermetically sealed chamber (1) communicated through valves with systems for supply and discharge of a fluid medium. The chamber has an opening (4) in which a sleeve (5) of flexible material is secured through one end along the perimeter, the sleeve being mounted in the chamber (1) with a possibility of reciprocation relative to the secured end so that during the motion from the initial position to the extreme position a part of the sleeve (5) is turned inside out forming a space (9) communicating with the chamber (1). The sleeve (5) through its other end is connected to a drum (7) disposed in the chamber (1) and mounted on a shaft (6) coupled to a reverser (11) through an overrunning clutch (8). In the initial position the sleeve (5) is wound on the drum (7).

Abstract: An improved energy-conserving servoactuator has at least one valve operatively associated with a double-acting fluid-powered actuator. When a load is applied to the actuator, the pressure in one actuator chamber will be greater than in the other. If the load is "opposing" with respect to the desired direction of actuator movement, fluid is supplied to the higher pressure chamber and is permitted to flow from the lower pressure chamber. However, if the load is "aiding" with respect to the desired direction of actuator movement, fluid in the higher pressure chamber is permitted to flow into the lower pressure chamber without drawing fresh fluid from the source.

Abstract: Electrically controlled combined valve/cylinder apparatus. The apparatus includes a housing having a cylindrical body and spaced first and second end walls closing the body. A cylinder is positioned inside the body and a piston is positioned inside the cylinder for reciprocal movement. A control ram connected to the piston extends through an aperture in the first end wall so that the piston is movable between a first position adjacent the first end wall in which the ram is extended and a second postion in which the piston is located adjacent the second end wall so that the ram is retracted. The apparatus further includes a cylindrical control sleeve positioned between and spaced from both the body and the cylinder. An inlet port tube is provided for supplying an electro-rheological fluid to the body while an outlet port tube is provided for discharging the fluid from the body.

Abstract: A device for feeding energy to a cylinder rotationally mounted on a stationary machine part includes a hydraulic pump disposed in the cylinder, and a transmission device located between the stationary machine part and the hydraulic pump, the transmission device being engageable with the hydraulic pump at a drive side thereof for driving the pump.

Abstract: The device comprises a pilot slide (27) controlled by a pressure differential (P-P') determined by an electromagnetic pilot valve element (43) located in a return circuit to a tank (7) which is common to both the hydraulic installation and a branch pipe (8). The device preferably includes an isolating valve (40) connected to the pilot valve element (43) so as to isolate a pilot chamber (30) in the event of a failure of the electromagnetic actuator.

Abstract: The object of the invention is to improve the position and feed or advance regulation of a hydraulic drive which is controlled by a proportional valve. In a first compensation circuit the flow characteristic of the proportional valve is linearized to obtain very small feed rates and a high control amplification. In a second compensation circuit the positioning error of the drive arising from the necessary overlapping of the proportional valve is compensated.

Abstract: An electronic tractor hitch control system in which the position of an implement hitch relative to a tractor can be set using a main control operable by a tractor operator from his normal location on the tractor and can also be set using a secondary control located at a location remote from the normal operator's location, such as on the rear of the tractor fenders. The system is arranged so that any implement position signal set using the secondary control is opposed by a smaller hitch positioning signal generated within the system so that the speed of movement of the hitch in response to hitch positions set using the secondary control is moderated. The system also includes circuitry for detecting short circuits in parts of the system located in vulnerable locations.

Abstract: Parallel, pulse-width-modulation controlled three-way valves each both supply and exhaust a pressure chamber of a fluid actuator. The phase difference of the oscillator carrier waves of the pulse width modulation input circuit effectively increases the frequency of a net actuator carrier wave so as to quicken the response of the actuator.

Abstract: A hydraulic actuator for automobiles includes a hydraulic actuator body composed of a hydraulic cylinder and a plurality of solenoid valves, and an electric control circuit disposed adjacent to the hydraulic actuator body for controlling the operation of the solenoid valves. The electric control circuit operates upon receipt of an execution signal, an analog desired-position signal, and an actual-position signal delivered from a position sensor. The hydraulic actuator thus constructed has an improved degree of compatibility.

Abstract: In hydraulic control devices comprising a two-way flow regulator in a resoir return passage, in which the flow regulator comprises a metering restriction and a pressure equalizer including a control piston with the piston ends disposed in control chambers and subjected to the action of control pressures, the actuation of a single-acting hydraulic motor under load often results in an unavoidable switching shock, because the displacement of the control piston involves the consumption of a certain volume of the pressure fluid. In order to eliminate the switching shock with a simple construction, the end of the control piston subjected to the action of the load pressure is formed as a closure element cooperating with a valve seat in the manner of a poppet valve for holding the load pressure.

Abstract: Disclosed is a pressure actuator such as a vacuum actuator comprising a valve unit including a plurality of solenoid valves and a diaphragm unit including a diaphragm defining a pressure chamber, air pressure within the pressure chamber being adjusted by selective activation of the solenoid valves which communicate the pressure chamber with pressure sources of different pressure levels, in which a casing of the actuator defines an accommodating chamber for accommodating the solenoid valve unit and a wall surface of the chamber is provided with ribs for guiding and positioning the solenoid valve unit inside the chamber. The ribs may be adapted to make a sliding contact with a side surface of the yokes of the solenoid valves and a smooth surface a printed circuit board which is attached to the solenoid valve unit. Alternatively or additionally, the ribs may be adapted to be fitted into a gap between a pair of adjacent yokes of the solenoid valves.

Abstract: A direct drive servo valve includes a housing and a series of conduits connecting the housing to a fluid pressure source and to an associated actuator, a sleeve in the housing having a plurality of passageways interconnecting the conduits and a spool valve member rotatable within the sleeve to connect the conduits as desired, the spool valve being rotated by a torque motor. The torque motor rotor is connected to the return side of the fluid pressure source. The sleeve is formed of a series of disks which have a desired pattern of holes therethrough and which are bonded together to create a manifold structure having the desired pattern of passageways. A rotary variable differential transformer is connected to the spool and provides feedback signals to an external circuit controlling the torque motor. A torque rod is connected to the spool and the housing to provide a preload which tends to center or "null out" the spool position when there is no input signal.

Abstract: A control system is provided for a hydraulic actuating system having a multi-phase stepping motor with a driver therefor which supplies and controls DC current through each of the motor windings such that no current is induced into the control winding from adjacent windings. The stepping motor precisely controls the rotation of an eccentric cam engaging an actuating plunger which actuates a control valve of the hydraulic actuating system. The driver receives control signals from a computer programmed to calculate, from user input command signals indicative of the desired system condition, and generate those control signals which most quickly achieve a rough approximation of the desired system condition. After this rough approximation is attained, the computer generates new control signals for the driver as a function of feedback signals and/or system component characteristics so as to precisely achieve the desired system condition.

Abstract: A hydraulic operated control system for remotely operating a walk-behind soil compactor. A remotely operated three-position valve is connected to the pressure line of the hydraulic system of the soil compactor and serves to control the flow of hydraulic fluid to opposite ends of a hydraulic cylinder unit that is operably connected to a hydraulic pump which operates the speed and direction control for the compactor. The cylinder unit includes a piston that is slidable within the cylinder and the piston is biased to a neutral position by springs. Through remote operation of the valve, hydraulic fluid will be directed to either end of the cylinder to provide direction and speed control for the compactor. A deadman switch is located on the remote control panel and manual release of the deadman switch will open the hydraulic circuit between the opposite ends of the cylinder to prevent fluid from being directed to the cylinder and will enable the springs to return the cylinder to a neutral no speed position.

Abstract: A control apparatus having a boom control system for controlling the movement of a liftable boom supported by a vehicle body and a working device control system for controlling a working device pivoted to the boom. Each of the control system includes a proportional solenoid valve and comprises an instruction circuit for producing an instruction signal in accordance with the amount of manipulation of an operating lever, discriminating circuit for determining the direction of operation of the valve from the instruction signal, a reference signal generator, a comparison circuit for comparing the instruction signal with the reference signal from the generator to obtain a pulse signal of a width in proportion to the amount of manipulation, and drive circuit for converting the pulse signal into a current to drive the valve in the direction determined by the discriminating circuit. The boom, as well as the working device, is movable at a speed corresponding to the amount of manipulation of the operating lever.

Abstract: The invention provides an improved method of operating a pulse-width-modulated solenoid valve so as to improve the proportionality of the flow-to-command pulse width characteristics of the valve. A train of command pulses (P.sub.1, P.sub.2, . . . P.sub.n), having widths corresponding to the desired flow through the valve, is superimposed on another train of pre-pulses (p.sub.1, p.sub.2, . . . p.sub.n). Each pre-pulse is timed to appear immediately ahead of an associated command pulse so that their widths will be effectively summed. The pre-pulses have widths necessary to substantially eliminate the "deadzone" in the flow-to-pulse width characteristics of the valve. Hence, the proportionality of the flow-to-command pulse width characteristics of the valve will be substantially improved.

Abstract: A digitally controlled air-over-hydraulic actuator includes a pneumatic cylinder and a hydraulic cylinder each having a separate piston and a common connecting rod. The pneumatic piston applies force to the connecting rod urging movement of the hydraulic piston. Bleeding of oil from one side of the hydraulic piston to the other is controlled by means of digital pulses applied to a digital valve that allows oil on either side of the hydraulic piston to flow to the other. The digital valve includes a moving piston having an oil passage that is momentarily aligned with ports to opposite sides of the hydraulic cylinder. A control system senses the differential pressure between opposite sides of the pneumatic piston to produce pulses that accelerate the digital valve piston past the ports, precisely controlling forced movement of the hydraulic piston.

Abstract: Method and apparatus of controlling and positioning a fluid actuator by supplying pressurized fluid to right and left actuating chambers of the actuator through an on-off control valves. To drive and position the actuator rapidly and accurately, the actuator can be driven at a higher speed by an initial driving force until it reaches near the desired position and continuously moved at a low speed by gradually increasing the fluid pressure to be supplied to the right and left actuating chambers of the actuator. The initial driving force in the high-speed range becomes maximum when the pressure is applied to one of the right and left actuating chambers while at the same time the other actuating chamber is exhausted. In the low-speed range and near the target position, the one actuating chamber is continuously supplied with the pressure while at the same time the other actuating chamber is gradually closed.