Showing papers on "Hydraulic machinery published in 2014"

High-Accuracy Tracking Control of Hydraulic Rotary Actuators With Modeling Uncertainties

Abstract: Structured and unstructured uncertainties are the main obstacles in the development of advanced controllers for high-accuracy tracking control of hydraulic servo systems. For the structured uncertainties, nonlinear adaptive control can be employed to achieve asymptotic tracking performance. But modeling errors, such as nonlinear frictions, always exist in physical hydraulic systems and degrade the tracking accuracy. In this paper, a robust integral of the sign of the error controller and an adaptive controller are synthesized via backstepping method for motion control of a hydraulic rotary actuator. In addition, an experimental internal leakage model of the actuator is built for precise model compensation. The proposed controller accounts for not only the structured uncertainties (i.e., parametric uncertainties), but also the unstructured uncertainties (i.e., nonlinear frictions). Furthermore, the controller theoretically guarantees asymptotic tracking performance in the presence of various uncertainties, which is very important for high-accuracy tracking control of hydraulic servo systems. Extensive comparative experimental results are obtained to verify the high-accuracy tracking performance of the proposed control strategy.

An Energy-Saving Pressure-Compensated Hydraulic System With Electrical Approach

Abstract: Mobile hydraulic systems are developed toward better control performance and higher energy efficiency. Pressure compensators, which govern the pressure drops over the control orifices, are widely used in multiactuator systems to improve their operability. However, additional energy is also dissipated in the compensators especially under the overrunning load conditions. This paper presents a novel energy-saving system, where the compensator is designed as a regeneration device consisting of a hydraulic motor and an electric generator. Then, hydraulic energy can be regenerated and pressure compensation function is realized by adapting the electromagnetic torque of the generator to the load as well. The close-loop control of the generator is designed by effective pressure drop estimation. The proposed energy-saving system and controller are implemented on an experimental platform of hybrid excavators which is equipped with an electric energy storage device. The experimental results show both good control performance and significant energy-saving effect.

Entropy Theory in Hydraulic Engineering: An Introduction

Abstract: \IEntropy Theory in Hydraulic Engineering: An Introduction\N is the first book to explain the basic concepts of entropy theory from a hydraulic perspective and demonstrate the theory’s application in solving practical engineering problems. In the hydraulic context, entropy is valuable as a way of measuring uncertainty or surprise —or even disorder or chaos— as a type of information. As hydraulic systems become more complex, entropy theory enables hydraulic engineers to quantify uncertainty, determine risk and reliability, estimate parameters, model processes, and design more robust and dependable water hydraulic systems.

Flow versus pressure control of pumps in mobile hydraulic systems

Abstract: This work studies an innovative working hydraulic system design for mobile applications, referred to as flow control. The fundamental difference compared to load-sensing systems is that the pump is ...

Nonlinear adaptive robust backstepping force control of hydraulic load simulator: Theory and experiments

Abstract: High performance robust force control of hydraulic load simulator with constant but unknown hydraulic parameters is considered. In contrast to the linear control based on hydraulic linearization equations, hydraulic inherent nonlinear properties and uncertainties make the conventional feedback proportional-integral-derivative (PID) control not yield to high performance requirements. Furthermore, the hydraulic system may be subjected to non-smooth and discontinuous nonlinearities due to the directional change of valve opening. In this paper, based on a nonlinear system model of hydraulic load simulator, a discontinuous projection-based nonlinear adaptive robust back-stepping controller is developed with servo valve dynamics. The proposed controller constructs a novel stable adaptive controller and adaptation laws with additional pressure dynamic related unknown parameters, which can compensate for the system nonlinearities and uncertain parameters, meanwhile a well-designed robust controller is also synthesized to dominate the model uncertainties coming from both parametric uncertainties and uncertain nonlinearities including unmodeled and ignored system dynamics. The controller theoretically guarantee a prescribed transient performance and final tracking accuracy in presence of both parametric uncertainties and uncertain nonlinearities; while achieving asymptotic output tracking in the absence of unstructured uncertainties. The implementation issues are also discussed for controller simplification. Some comparative results are obtained to verify the high-performance nature of the proposed controller.

A dynamical system perspective on plant hydraulic failure

Abstract: Photosynthesis is governed by leaf water status that depends on the difference between the rates of transpiration and water supply from the soil and through the plant xylem. When transpiration increases compared to water supply, the leaf water potential reaches a more negative equilibrium, leading to water stress. Both high atmospheric vapor pressure deficit and low soil moisture increase the water demand while decreasing the supply due to lowered soil-to-root conductance and xylem cavitation. Therefore, dry conditions may eventually reduce the leaf water potential to the point of collapsing the plant hydraulic system. This “hydraulic failure” is shown to correspond to a fold bifurcation where the environmental parameters (vapor pressure deficit and soil moisture) trigger the loss of a physiologically sustainable equilibrium. Using a minimal plant hydraulic model, coordination among plant hydraulic traits is shown to result in increased resilience to environmental stresses, thereby impeding hydraulic failure unless hydraulic traits deteriorate due to prolonged water shortage or other damages.

A Hydraulic Wind Power Transfer System: Operation and Modeling

Abstract: Conventional wind power plants employ a variable speed gearbox to run a generator housed on top of a tower. A new topology can remove some of the weight from the tower and centralize the wind power generation. This new topology uses a hydraulic wind power transfer system to connect several wind turbines to the generation unit. This paper demonstrates a mathematical modeling of this wind power transfer technology and its dynamic behavior. The flow response, angular velocity, and pressure of the system obtained from the mathematical model are compared with test results to demonstrate the accuracy of the mathematical model. Several speed-step responses of the system obtained from the mathematical model demonstrate a close agreement with the results from the prototype of the hydraulic wind power transfer unit.

An effective heave compensation and anti-sway control approach for offshore hydraulic crane operations

Abstract: Offshore hydraulic cranes are difficult to operate safely, accurately and efficiently due to their heavy structure, large inertia, non-intuitive control interface and load sway issues that result from external disturbances. This paper presents an effective heave compensation and anti-sway control approach for offshore crane operations, which is based on robotic arm kinematics and energy dissipation principles. Unlike common operator-based joint-by-joint control procedures, this automated method is more flexible, allowing for more intuitive crane operations and more accurate positioning of the hoisted load. In particular, a unique feature of this approach is that the two control functions of heave compensation and anti-sway are transparently combined and simulated in an integrated modelling environment. The system architecture integrates the control model for crane operations, the hydraulic system model for hydraulics characteristic analysis, the 3D model of the crane to be controlled, the vessel and the environment for visualisation. The proposed control algorithm and simulation model can be extended to any type of crane model regardless of its configuration or degree of freedom (DOF) without influencing the effectiveness of the method. The hydraulic model is built by using Bond Graph elements and integrated with the control model in the 20-sim simulation environment. The crane operation can be simulated and controlled by the operator using a 3-axis joystick, which provides a transparent user interface. Related simulations were carried out to validate the efficiency and flexibility of the system architecture. As a case study, a 3joints knuckle boom crane was implemented and tested. The simulation results prove the presented control algorithm for heave compensation and anti-sway to be a valid and efficient solution. Index Terms – offshore hydraulic crane, heave compensation, anti-sway, modeling and simulation

Theoretical and experimental studies of a switched inertance hydraulic system

Abstract: A switched inertance hydraulic system uses a fast switching valve to control flow or pressure and is potentially very efficient as it does not rely on dissipation of power by throttling. This article studies its performance using an analytical method which efficiently describes the system in the time domain and frequency domain. A lumped parameter model and a distributed parameter model have been used for investigation using different parameters and conditions. The analytical models have been validated in experiments and the results on a prototype device show a very promising performance. The proposed analytical models are effective for understanding, analysing and optimizing the characteristics and performance of a switched inertance hydraulic system.

Optimisation and control of a hydraulic power take-off unit for a wave energy converter in irregular waves:

Abstract: The optimisation of a wave energy converter hydraulic power take-off for sea states of varying wave amplitude, direction and frequency is a significant problem. Sub-optimal configuration can result in very inefficient energy conversion, so understanding the design trade-offs is key to the success of the technology. This work focuses on a generic point absorber type wave energy converter. Previous work by the authors has considered the optimisation of this device for regular waves to gain an understanding of the fundamental issues. This work extends the analysis to the more realistic case of irregular waves. Simulations are performed using an irregular wave input to predict how the power take-off will operate in real sea conditions. Work is also presented on a motor speed control strategy to maintain the maximum flow of electrical power to the grid, assuming the use of a doubly fed induction generator. Finally, the sizing of key components in the power take-off is considered in an attempt to maximise power take-off efficiency and generated power.

Four-column oil-pressure square pipe punching equipment

Abstract: The invention relates to four-column oil-pressure square pipe punching equipment and belongs to the field of automatic processing of mechanical equipment. The four-column oil-pressure square pipe punching equipment comprises a machine frame, a feeding/discharging device, a punching device, a punching working platform, a hydraulic power device and a programmable logic controller (PLC) electric cabinet, wherein the hydraulic power device provides power; the PLC electric cabinet controls the procedure processing process; the machine frame is arranged at the lower part of the equipment; the feeding/discharging device is placed on the machine frame; the punching working platform is fixedly connected to the machine frame and is mounted below the feeding/discharging device; the punching device is arranged above the punching working platform. The equipment finishes feeding, positioning, stepping punching and discharging through the PLC electric cabinet and realizes the punching operation on a square pipe. The equipment has the characteristics of high efficiency, high quality and simple structure, can reduce the labor intensity, can adjust the hole position and quantity according to requirements, and can adapt various punching requirements of the square holes.

High-Accuracy Range Detection Radar Sensor for Hydraulic Cylinders

Abstract: Industrial automation requires highly precise distance measurement sensors. Accurate detection of the piston position is indispensable for the control and monitoring of hydraulic cylinder applications. Known external and integrated solutions are subject to many limitations as for example in accuracy, in measurement length, or in price. A promising approach consists in the use of precise and low-cost radar sensors. The developed K-band frequency modulated continuous wave (FMCW) radar system in this paper detects the piston position in a hydraulic cylinder based on the guided propagation of a radar signal. The dielectric characteristics of the hydraulic oil are obtained for this purpose by permittivity measurement methods. Influences of the hydraulic oil on wave propagation in cylindrical waveguides as well as mechanical requirements associated with this new approach are investigated. The design of an adapted oil- and pressure-resistant transition between the radar sensor and the hydraulic cylinder and a novel calibration method will be described and verified under real measurement conditions. At a measurement repetition rate of 2 kHz, an accuracy of well below 200 μm was achieved for a hydraulic cylinder of 1 m in length.

Output Regulation of Large-Scale Hydraulic Networks

Abstract: The problem of output regulation for a class of hydraulic networks found in district heating systems is addressed in this brief. The results show that global asymptotic and semiglobal exponential output regulation is achievable using a set of decentralized proportional-integral controllers. The fact that the result is global and independent of the number of end users has the consequence that structural changes such as end-user addition and removal can be made in the network while maintaining the stability properties of the system. Furthermore, the decentralized nature of the control architecture eases the implementation of structural changes in the network.

Connecting rod for a two-stage variable compression

Abstract: A connecting rod for a two stage variable compression in an internal combustion engine, the connecting rod including a combustion piston pin support eye that is arranged offset relative to an axis in an eccentrical component which is pivotable about the axis in a first direction of rotation through a first hydraulic displacement cavity and pivotable in a second direction of rotation through a second hydraulic displacement cavity, wherein a hydraulic valve is arranged in the connecting rod, wherein the hydraulic valve includes a hydraulic supply connection at which a hydraulic pressure is applied, wherein the hydraulic pressure moves a hydraulic piston against a force of a preload of a spring, wherein the hydraulic piston remains in a stable low pressure position in a low range of the hydraulic pressure due to the preload of the spring, wherein the supply connection is hydraulically connected with the first hydraulic displacement cavity in the low range of the hydraulic pressure, wherein the hydraulic piston continues to contact a stop at a housing in a high range of the hydraulic pressure due to a pressure applied to a hydraulic piston surface, wherein the supply connection is connected with the second hydraulic displacement cavity in a stable high pressure position of the hydraulic piston in the high range of the hydraulic pressure.

High power density integrated electro-hydraulic energy converter for heavy hybrid off-highway working vehicles

Abstract: Novel high power density integrated electro-hydraulic machine for electrical hybrid working vehicles is presented. The machine is dedicated to be used as a mechanical power source for hydraulic actuators with possibility of electrical energy recuperation. Advantages of using such a machine in mobile environments are discussed. The efficiency of the device is studied and compared with the traditional valve controlled systems.

Dynamic Characteristics of Pressure Compensator in Underwater Hydraulic System

Abstract: A pressure compensator for an underwater hydraulic system is studied in this paper. The compensator is used to maintain the tank pressure of the underwater hydraulic system so that it is slightly greater than the ambient pressure, allowing the system to work at any depth. The dynamic characteristics of the pressure compensator are studied using theoretical analysis, simulation and experiment. The tank pressure changes due to the step flow to the tank coming from the motion of a piston in a single-rod cylinder. This flow is caused by the unequal areas of the piston. The tank pressure change can be mathematically determined. A design procedure focusing on the dynamic characteristics of the pressure compensator is given. A compensator and underwater hydraulic system were built and the dynamic characteristics of the compensator were tested. Both simulation and experimental results conform to the analysis. The study provides a theoretical way to determine the dynamic characteristics of a pressure compensator in an underwater hydraulic system.

Pressure measurements and high speed visualizations of the cavitation phenomena at deep part load condition in a Francis turbine

Abstract: In a hydraulic power plant, it is essential to provide a reliable, sustainable and flexible energy supply. In recent years, in order to cover the variations of the renewable electricity production, hydraulic power plants are demanded to operate with more extended operating range. Under these off-design conditions, a hydraulic turbine is subject to cavitating swirl flow at the runner outlet. It is well-known that the helically/symmetrically shaped cavitation develops at the runner outlet in part load/full load condition, and it gives severe damage to the hydraulic systems under certain conditions. Although there have been many studies about partial and full load conditions, contributions reporting the deep part load condition are limited, and the cavitation behaviour at this condition is not yet understood. This study aims to unveil the cavitation phenomena at deep part load condition by high speed visualizations focusing on the draft tube cone as well as the runner blade channel, and pressure fluctuations associated with the phenomena were also investigated.

Development of a dual-acting axial piston pump for displacement-controlled system:

Abstract: Pump-controlled hydraulic systems can effectively eliminate throttling losses, but one issue is the unequal flow rate through an asymmetric actuator, which is widely used in hydraulic systems. In t...

Hydraulic system for construction machine

Abstract: The present disclosure relates to a hydraulic system for a construction machine, and more particularly, to a hydraulic system for a construction machine including a plurality of actuators, in which each of the actuators includes a pump/motor, is operated under a control of a corresponding pump/motor, and stores working oil in an accumulator or receives the working oil supplemented from the accumulator in accordance with a difference between a flow rate entering the actuator and a flow rate discharged from the actuator.