Showing papers on "Hydraulic machinery published in 1999"

Adaptive robust motion control of single-rod hydraulic actuators: Theory and experiments

Abstract: High performance robust motion control of single-rod hydraulic actuators is considered. In contrast to the double-rod hydraulic actuators studied previously, the two chambers of a single-rod hydraulic actuator have different areas. As a result, the dynamic equations describing the pressure changes in the two chambers cannot be combined into a single load pressure equation. This complicates the controller design since it not only increases the dimension of the system to be dealt with but also brings in the stability issue of the added internal dynamics. A discontinuous projection based adaptive robust controller (ARC) is constructed. The controller is able to take into account not only the effect of parameter variations coming from the inertia load and various hydraulic parameters but also the effect of hard-to-model nonlinearities such as uncompensated friction forces and external disturbances. Extensive experimental results are obtained for the swing motion control of a hydraulic arm. In comparison to a state-of-the-art industrial motion controller, the proposed ARC algorithm achieves more than a magnitude reduction of tracking errors. Furthermore, during constant velocity and regulation periods, the ARC controller reduces the tracking errors almost down to the measurement resolution level.

Experiments and simulations on the nonlinear control of a hydraulic servosystem

Abstract: This paper presents the derivation, simulation, and implementation of a nonlinear tracking control law for a hydraulic servosystem. An analysis of the nonlinear system equations is used in the derivation of a Lyapunov function that provides for exponentially stable force trajectory tracking. This control law is then extended to provide position tracking. The proposed controller is simulated and then implemented on an experimental hydraulic system to test the limits of its performance and the realistic effects of friction.

Solar collector tracking system

Abstract: A solar collector tracking system that has a solar collection device having multiple lens assemblies mounted on its front surface. An exoskeleton structure is secured to the rear surface of the solar collection device and it is pivotally secured about a horizontal axis to the front end of an azimuth platform assembly. A hydraulic elevation actuator is pivotally mounted in the azimuth platform assembly about a horizontal axis and the front end of its piston rod is pivotally connected to the rear surface of the solar collection device and this allows it to be pivoted approximately 90 degrees between a vertical operating position and a horizontal storage position. The azimuth platform assembly is journaled on the top end of a tower extending up from the ground. A tubular post is rigidly secured to the top end of the post. A drive head extends horizontally from the tubular post and it has a pivot pin that extends upwardly therefrom. A primary and a secondary azimuth hydraulic actuator have the front ends of their respective piston rods coupled to the pivot pin. The opposite ends of the azimuth hydraulic actuators are pivotally secured to the interior of the azimuth platform assembly. A hydraulic power unit is connected to the respective hydraulic actuators. An electronic controller monitors signals from an azimuth encoder sensor and an elevation encoder sensor and it directs the respective hydraulic actuators to move their respective piston rods inwardly and outwardly so that the solar collection device can be rotated to track the rays of the sun.

Study of hydraulic transients in hydropower plants through simulation of nonlinear model of penstock and hydraulic turbine model

Abstract: Study of hydraulic transients in hydropower plants specifically in hydraulic turbine units, with penstock, spiral case and draft tube-is necessary due to power and frequency oscillations which normally occur in generator units, mainly during load rejections. In turn, this causes large pressure and subpressure oscillations in turbine hydraulic systems and must be evaluated to avoid mechanical failures. In this context, this work analyses discrete hydraulic systems with emphasis on hydraulic parameter analysis. The simulation used was developed based on analog mathematical models of transient phenomenon equations and on a hydro turbine model. The results were obtained by using a nonlinear analog-digital simulation method. Comparisons between results of a theoretical simulation of a literature example using the characteristics method and the results obtained with the present method are presented. Theoretical simulation results obtained from a 360 MW turbine and experimental results are also confronted.

Efficient inverse transient analysis in series pipe systems

Abstract: Measurement of the changes in heads initiated by a valve closure are used to calibrate the friction factors in a hydraulic system consisting of a series-connected pipeline and a downstream valve joining two reservoirs. The calibration is performed by minimizing the inverse least-squares problem representing the difference between the measured and predicted transient response in the network. The hydraulic transient is modeled using the method of characteristics. Unlike previous approaches, the sensitivity information required for the minimization or error is obtained by direct differentiation of the method of characteristic equations and the valve equation with respect to the friction factors. The sensitivity of the calibration results to the amount of data included in the analysis, the initial friction factor estimates, and modeling and simulated measurement errors is discussed.

Dual redundant active/active brake-by-wire architecture

Abstract: The braking control system provides dual redundant control of hydraulically operated wheel braking for an aircraft. A primary hydraulic system provides hydraulic power for normal operation of the plurality of wheel brakes, and a secondary hydraulic system provides hydraulic power for alternate operation of the plurality of wheel brakes. A control unit is provided for controlling brake pressure communicated to the wheel brakes through the primary and secondary hydraulic systems, and a monitor channel is operatively connected to the primary hydraulic system for detecting faults in the primary and secondary hydraulic systems and for selecting between the primary and secondary hydraulic systems for providing braking pressure. The monitor channel detects occurrence of loss of pressure in the primary hydraulic system, if any brake has unwanted pressure applied, and if a fault is detected on the primary or secondary channels that affects more than one wheel brake on each landing gear. The primary hydraulic system comprises at least one primary hydraulic fluid control channel and at least one secondary hydraulic fluid control channel, the primary and secondary fluid channels being redundant and partitioned among the plurality of wheel brakes so that even if both the primary and secondary channels fail to apply pressure, braking will be lost to only a portion of the wheel brakes and the loss will be in a symmetrical pattern, and the secondary hydraulic system comprises at least one primary hydraulic fluid control channel and at least one secondary hydraulic fluid control channel.

Hydraulic well control system

Abstract: A system for transmitting hydraulic control signals and hydraulic power to downhole well tools while reducing the number of hydraulic lines installed in the wellbore. Hydraulic control signals can be furnished at relatively lower pressures, and the hydraulic pressure within the line can be selectively increased over a threshold level to provide hydraulic actuation power. The system can provide multiple control paths through a few number of hydraulic lines to provide flexibility and verification of well tool operation. Closed loop hydraulic operation monitors well tool operation, and a combination of pressurized hydraulic lines can provide an operating code for selective downhole well tool control. Four hydraulic lines can provide independent control and actuation of seven well tools, and additional combinations can be constructed.

Nonlinear modeling and validation of solenoid-controlled pilot-operated servovalves

Abstract: Solenoid-controlled pilot-operated servovalves are flow control devices widely used to drive high-flow hydraulic actuators in heavy-duty off-highway machinery. In these applications, a spool-operated pilot stage is required to account for large flow force in the main hydraulic valve. Design optimization, performance improvement, and fault diagnosis of such complex two-stage servovalves often require sophisticated analytical models with accurate physical parameters. The paper presents a step-by-step methodology for nonlinear modeling, parameter determination, model validation, and performance evaluation of solenoid-controlled pilot-operated spool valves. The proposed model takes into account such nonlinearities as pilot spool dead band, spool friction, flow coefficient variability, and leakage. This new model is complete in the sense that all nonlinear interactions between various electromechanical elements have been incorporated in a compact yet comprehensive model. The simulation model accepts a command voltage to the solenoids as input and gives the second stage spool displacement as output. To obtain the physical parameters used in the valve model, a systematic approach is proposed based on state measurement and curve-fitting techniques. The identified parameters of an example valve were used in simulations both to validate the nonlinear valve model and also to assess the valve's performance when certain valve parameters change.

Mobile working machine

Abstract: The present invention relates to a mobile handling device with hydraulic circuit, which hydraulic circuit comprises a lifting cylinder (1) arranged in a lifting device (100) suitable for handling a variable load and an accumulator (6) for recovering or recycling lowering load energy, the hydraulic circuit also comprising a variable hydraulic machine (3) with two ports (10, 11), which hydraulic machine is capable via a drive unit (D) of emitting full system pressure in two flow directions to said ports, one port (11) being connected to said accumulator (6) and the other port being connected to said lifting cylinder.

Hydraulic control systems

Abstract: A vehicle suspension system comprising a hydraulic roll control actuator 4 controlled by a hydraulic circuit 10. The circuit 10 includes a valve block having a pressure line 18 a supplied by a pump 12 and a return line 20 a, and a pressure control valve 22 for controlling the flow of hydraulic fluid from the pressure line 18 a to the return line 20 to control the hydraulic pressure drop between them. Two actuation control valves 24, 26 allow connection of the actuators between the pressure and return lines to control the actuating force produced by the actuators. A control unit 30 is arranged to connect the actuators 4 only when the desired actuating force is greater than a minimum value corresponding to a minimum pressure drop which can be produced by the pressure control valve 22, and to determine the minimum pressure drop from measurement of the temperature of a part of the hydraulic system.

Control device for hydraulically-operated equipment

Abstract: Workability and operability of hydraulically-operated equipment is enhanced by optimally changing in accordance with the work content a responsiveness of an output signal relative to an input signal of each hydraulic control device, which constitutes a hydraulic system, at times heightening quick reaction capabilities, and at other times heightening steadiness. As a quantity of state of a load pressure signal of a hydraulic actuator, for example, is inputted to a response suppressing portion, and in accordance with a high-pass filter, a higher frequency fluctuation component in a pressure signal is extracted. An operation quantity of an operation lever, for example, is inputted from a suppression quantity specifying portion, and a frequency domain extracted by the high-pass filter is changed so as to become a narrow range of greater than a higher frequency in accordance with an operation quantity becoming larger, and further, so as to become a broad range of greater than a lower frequency in accordance with an operation quantity becoming smaller. Then, a compensation operation is performed, which subtracts from a flow command to a response suppression target apparatus, a signal of a high frequency component of a hydraulic actuator load pressure, and a compensated flow command is outputted to the response suppression target apparatus.

Magnetically-latchable fluid control valve system

Abstract: A hydraulic valve control system that includes a plurality of digitally actuated magnetically-latchable four-way valves that directly or indirectly control the position of a hydraulic actuator. The digitally actuated magnetically-latchable four-way valves are controlled by a controller that can control the valves in accordance with a servo routine. The servo routine may include the computation of a plurality of cost functions and the selection of an action that corresponds to the lowest cost.

Hydraulic noise reduction assembly with variable side branch

Abstract: A variable volume side branch is provided or attenuating fluid noise in a hydraulic system having a fluid pump and includes a variable volume fluid container having a fluid inlet and a fluid outlet The fluid container is operable to change the volumetric thereof and to thereby attenuate fluid noise in a hydraulic system in response to changes in fluid pump speed The fluid inlet of the variable volume fluid container is in fluid communication with a fluid pump and control of the fluid container volumetric is accomplished through the use of a speed sensor, a controller and various actuating mechanisms The speed sensor determines fluid pump speed and transmits a signal indicative thereof to a controller coupled thereto The controller is operable to receive an input signal from the speed sensor and to output an appropriate signal to the actuating mechanism to change the volumetric length of the fluid container in response to the input signal This assembly optimally attenuates fluid noise in a hydraulic system which includes the present variable side branch

Hydraulic system having boost pump in parallel with a primary pump and a boost pump drive therefor

Abstract: A hydraulic circuit having a boost pump in series with a primary (tractor) hydraulic source provides additional fluid power to operate an aircart fan in an air seeding system for which a tractor hydraulic system does not have enough fluid power capacity. The boost pump raises the pressure of the flow delivered to the fan motor up from that pressure delivered from the tractor to a higher pressure. Tractor pressure is supplied to the boost pump inlet, the boost pump is driven by ground engaging wheels of the aircart, and the resulting flow to the aircart fan motor is increased in pressure by the boost pump.

Hydraulically actuated power takeoff clutch assembly

Abstract: A hydraulically actuated power takeoff clutch assembly is rigidly coupled to the flywheel of an engine and has an input hub which serves as a gear to drive auxiliary hydraulic pumps. The input hub is a portion of a wet clutch which is hydraulically actuated through a rotary union connected to an output shaft. The serviceable parts of the clutch are secured to the output shaft and are separably removable from the hydraulic power takeoff assembly for servicing. The clutch is of a multiple disk type. An electronic controller monitors the input and output speeds of the hydraulic power takeoff device and is effective to “bump” the unit to accomodate high inertia loads and to further monitor the operation of the device, such that the clutch thereof serves as a torque limiter.

Investigation of reliability of hydraulic-robots for hazardous environments using analytic redundancy

Abstract: The Rosie mobile worksystem is a robot that is on the cutting edge of hazardous environment robotics. It is a heavy-duty hydraulic robot designed for nuclear reactor decontamination and dismantlement. The robot consists of a wheeled platform containing a central hydraulic power supply powered by an electric tether, four independently steerable wheels, and a heavy-duty crane/manipulator. The hydraulic wheel actuator subsystem has been determined to be a vital component of the mobile platform through reliability analysis. Our research into analyzing this robot's reliability through the technique of analytical redundancy (AR) will help provide the Department of Energy (DOE) with a more complete and effective set of tests for monitoring and diagnostics of the Rosie system. In this paper, we discuss the derivation through AR of a suite of model based tests for the default sensor package for one of Rosie's wheel actuators. AR allows us to exploit the sensor information of the sensors values and the system model to derive tests of the consistency of the sensor data. Some of these tests are comparison of the actual system response to control inputs to predicted response indicated by the model, the other tests uncovered by the AR analysis reflect higher order state interdependencies. These tests and their use in monitoring and diagnostics for Rosie are detailed and examined in depth. This work is also an interesting example of the application of model based techniques for an important class of practical systems.

Variable pressure relief system for hydraulically actuated limited slip differentials

Abstract: The present invention relates generally to hydraulically actuated limited slip differentials. More particularly, the present invention relates to a hydraulic limited slip differential which utilizes a variable pressure relief check valve used to vary the maximum hydraulic pressure available within the differential case in a manner that the limited slip feature can be adjusted anywhere between a full “ON” and a full “OFF” configuration. Hydraulic fluid will not flow through the check valve until the hydraulic pressure within the case results in a reaction force larger than the check valve activation pressure, thus providing a maximum pressure limit in the hydraulic system. The activation pressure of the check valve can be selectively controlled by an actuator. The movement of the actuator corresponds to a change the retaining force of the check valve. Dynamic control of the system in response to vehicle operational parameters may also be performed.

Feed control hydraulic circuit for wood chipper attachment

Abstract: A hydraulic circuit for a wood chipper attachment for a skid steer loader provides power to both a motor for driving a chipper wheel and a motor for driving a feed roller. A priority flow valve is provided to supply priority of flow to the chipper motor. As pressure increases on the chipper motor, the output from the skid steer loader pump reduces and the priority flow valve acts to reduce flow to the feed motor to reduce the infeed speed. The wood chipper is adapted to be mounted on a skid steer loader and utilize the hydraulic power source from the loader power source. A separate relief valve for the chipper wheel motor is set to relieve pressure if the chipper wheel motor stalls at a lower pressure than the relief valve for the hydraulic system on the skid steer loader so that the feed motor will have sufficient pressure for reversing the feed wheel.

Fluid regeneration circuit for hydraulic cylinders

Abstract: A fluid regeneration circuit for a hydraulic system having at least one hydraulic actuating cylinder associated therewith, the present circuit including a control valve connected in fluid communication with the actuating cylinder for controlling the operation thereof, a regeneration valve connected in fluid communication with the control valve and with the head and rod end portions of the cylinder, a position sensor coupled to the actuating cylinder for sensing the position of the piston within the cylinder during movement thereof, and a controller coupled to the position sensor, the control valve and the regeneration valve for controlling fluid flow to and from the actuating cylinder. The controller is operable to receive signals from the position sensor and determine the velocity of the piston based upon the signals outputted by the position sensor, and it is operable to output appropriate signals to the regeneration valve to regenerate fluid flow to the head end portion of the actuating cylinder when the velocity of the piston is determined to be above a first predetermined threshold velocity, and to discontinue fluid flow to the head end portion of the actuating cylinder when the velocity of the piston is below a second predetermined threshold velocity.

Hydraulic system for a detachable implement

Abstract: A hydraulic system for a detachable implement such as draper platform for a combine utilizes a platform-mounted pump supplied with return oil from the existing reel drive motor. The system utilizes the existing combine hydraulic connection for the reel drive to supply oil to the draper belt drive motors. Oil from the combine powers the reel drive motor and then flows into a manifold block (mixing chamber) before entering the inlet of the draper belt drive pump. This pump is sized to provide sufficient oil flow to power the draper belt drive motors, arranged in series. Return oil from the belt drive motors is routed back to the manifold block where it can mix with incoming oil from the reel drive pump before returning to the combine reservoir or being recirculated to the belt drive motors. The hydraulic system avoids the need to equip the platform with a complete hydraulic system and avoids the need to modify the existing hydraulic system of the combine.

Multiple line hydraulic system flush valve and method of use

Abstract: A flush valve for a multiple line hydraulic system includes a bifurcated manifold, the bifurcation being provided by a piston actuatable hydraulically, mechanically, electrically magnetically or by fiber optic means. The piston or gate is provided with a port extending diametrically therethrough and oriented to become coaxial with an inlet and outlet of the manifold upon actuation of the piston. With the port aligned the hydraulic fluid in the system can be displaced by fresh fluid. The piston is then deactivated which results in the port becoming misaligned with the inlet and outlet of the manifold. In this condition the hydraulic system is again sealed and functions normally.

Hydraulic actuator control with open-centre electrohydraulic valve using a cerebellar model articulation controller neural network algorithm

Abstract: Real-time learning control of a hydraulic actuator is studied using a cerebellar model articulation controller (CMAC) neural network architecture. Experiments are conducted on a one-degree-of-freedom hydraulic cylinder. The main applications considered are the earth-moving equipment applications. The electrohydraulic valve used to control the flow in the hydraulic circuit is an open-centre non-pressure-compensated type of valve, the type used in most earth-moving vehicles. Large hysteresis and dead band are observed in the hydraulic system which result in a large delay and poor dynamic tracking performance. A comparison of the experimental results on the control of the hydraulic actuator for the CMAC controller and a conventional proportional-integral controller with a model-based feedforward valve transform is made.

Hydrostatic drive system for an injection molding machine and a method for operating such a drive system

Abstract: The aim of the invention is to create a hydrostatic drive system for the mobile mold closing plate (10) of an injection molding machine in which only small amounts of unusable energy are lost. To this end, the hydraulic pump (19) can deliver a pressure medium in a compressed-medium ductwork system (17, 24) comprising a hydraulic accumulator (24), and the first pressure chamber (15) of the hydraulic cylinder (11) is connected to the compressed-medium ductwork system (17, 24). In addition, the hydraulic cylinder (11) is controlled by a hydraulic transformer (18) which is basically constructed in any manner. Said hydraulic transformer is located with the primary pressure connection (32) thereof on the compressed-medium ductwork system (17, 24). Pressure medium can be fed to the second pressure chamber (16) of the hydraulic cylinder (11) or can be carried away from the second pressure chamber (16) via the secondary pressure connection (34) of the hydraulic transformer. According to the inventive hydrostatic drive system, the rapid, high demand for pressure medium from the hydraulic accumulator (24) when the mold closing plate (10) closes during the acceleration phase can, to a large extent, be covered. When braking the mold closing plate (10), the hydraulic transformer (18) can assist in refilling the hydraulic accumulator (24). The hydraulic accumulator (24) can be filled again by the hydraulic pump (19) during idle times in which the mold closing plate (10) is in an non-operating state.

Nonlinear optimal control of an open-channel hydraulic system based on an infinite-dimensional model

Abstract: A nonlinear optimal control approach based on an infinite-dimensional model is presented which determines the optimal opening of a regulator gate at the upstream end in the case of a single reach hydraulic system, in order to minimize the waste water and the variation of the water depth. The effectiveness of the control algorithm is demonstrated by a simulation example. The simulation results show good improvements in reducing the variation of water depth compared to the uncontrolled case. The Saint-Venant equations and their adjoint equations have been solved numerically by using a nonlinear implicit integration scheme (the Preissmann scheme). Our main contribution is the solution of an open-channel control problem which includes a distributed parameter model, with nonlinearities, friction, canal slope, an adjustable regulator gate and a pumping station, via variational calculus.

Leakage fault diagnosing method for hydraulic system

Abstract: A method for diagnosing the leakage failure of hydraulic system based on pressure waveform in pressure cavity features that the Bernoulli equation for the deformation existing between instantaneous flow rateat orifice and pressure or equivalent liquid transfer is used to derive the instantaneous flow formula of hydraulic oil leaked from the hydraulic part to be tested when external or internal leakage exists, the accumulated flow of the cavity of the hydraulic part to be tested is determined by integration, and the parameters of hydraulic system itself, such as rated flow, are used to diagnose the leakage failure. Its advantages are no need of modifying original system, low cost and high precision.

Flexible hoses communicating with a deployable hydraulic power assembly

Abstract: A hydraulic power assembly is comprised of a hydraulic pump being attached to and powered by a ram air turbine. A strut is rotatably attached to an aircraft by having one end mounted on a trunion, and the hydraulic power assembly affixed to the other, distal end. Flexible hoses fluidly communicate the pump with a hydraulic interface located inside of the aircraft. The hydraulic interface fluidly communicates with the aircraft's hydraulic system. The hydraulic power assembly and the strut are normally stored within the fuselage of the aircraft and are deployable into an adjacent airstream in an emergency.