Pressures In Cylinder Chambers Research Articles

Extended State Observer-Based Fuzzy Adaptive Backstepping Force Control of a Deep-Sea Hydraulic Manipulator with Long Transmission Pipelines

The force tracking control of deep-sea hydraulic manipulator systems with long transmission pipelines is disposed via fuzzy adaptive backstepping control based on an extended state observer in this paper. The pipeline model is established and then used to estimate the pressures in cylinder chambers, which are used to obtain the output force. In this process, the velocity of the piston, which is unmeasured, is needed, and an extended state observer is constructed to estimate the unmeasurable velocity signal. To cope with parameter uncertainties caused by changes in working depth, an adaptive algorithm is combined with the backstepping controller. Fuzzy logic is employed to design self-tuners that can automatically adjust the control parameters to guarantee force control performance from shallow seas to deep seas. The experimental results illustrate the success of the proposed control method. Comparative experimental results demonstrate that the extended state observer-based fuzzy adaptive backstepping controller has a relatively better tracking performance in different working conditions.

Synchroniser control with proportional pressure reducing valves and displacement feedback

In order to improve the shift quality of automatic transmission with synchroniser, a synchroniser electrohydraulic control system equipped with the proportional pressure reducing valves is proposed. The principle of the control system is introduced in detail. The PID controller is used to realise closed-loop control of shift displacement to achieve the synchronisation. A numerical model and a test apparatus have built up to validated the control performance. The simulated and measured engagement and disengagement of the synchroniser with the proposed control system are investigated in detail. The results indicate that the shift displacement is controllable by changing the cylinder chamber pressure. The back pressure value is useful for a smooth synchroniser operation. It is determined by the sleeve motion and the throttle parameter. The back pressure affects little on the synchronisation stage during the engagement process. The proposed method can be used for the optimising design of the electrohydraulic system for the synchroniser control.

Virtual sensing of load forces in hydraulic actuators using second- and higher-order sliding modes

External load forces are challenging for sensing or estimating in the hydraulic actuators. Once it is due to inconvenient instrumentation of the force sensors, especially on an open-end mechanical interface. The other way, the complex nonlinear system behavior aggravates reconstructing the system states in a robust and real-time suitable manner. This paper proposes a sensorless estimation of external load forces in standard hydraulic actuators by using a well-established equivalent output injection of the second-order sliding mode and also higher-order sliding mode differentiator. Only the basic inertial and frictional parameters are assumed to be known from an initial identification without external load. Afterwards, the robust exact differentiators are used in order to reconstruct the system states. Noisy signals of the cylinder chamber pressures and piston stroke are the single quantities available from the measurement. An experimental case study, accomplished on the setup of two hydraulic cylinders arranged and operated in antagonistic way, is provided. The force-cell on the rigid interface between both cylinders is used for reference measurements and evaluation of the estimation algorithms. Two estimation approaches, one of the 2nd and another of the 4th order, are assessed in performance and compared to each other along with discussion.

Digital hydraulic single-link trajectory tracking control through flow-based control

Recent advancement in controllability of digital hydraulic is similar to the performance of a proportional/servo hydraulic system, and several studies show that digital hydraulic will be an alternative for proportional/servo hydraulic. In this paper, tip point tracking of a single-link arm is taken as the subject of the study. Here, the single-link arm is controlled by a digital hydraulic system, which is established with parallel-connected on/off valves. In order to attain stepwise flow control, the pulse code modulation technique is used. By referring to the previous work, the control signal for the trajectory tracking is calculated by taking account of cylinder chamber pressure and velocity. But in this study, the required volume flow rate for trajectory tracing is taken into account for generating control signal. This approach improves the performance of the digital hydraulic system at lower velocity tracking and also reduces the computational complexity. The analysis is conducted with the proposed algorithm for 4-bit and 5-bit digital flow control units and tip point response of single link is presented. The results show that the 5-bit system has significantly better performance than the 4-bit system. In addition, the analysis is conducted with different stroke lengths such as 200, 100 and 50 mm for studying the behaviour of the system at lower velocity tracking. Better controllability is achieved at lower velocity tracking, and the results obtained with the proposed algorithm have nearly 2% tracking error.

A dual EHA system for the improvement of position control performance via active load compensation

The dynamic response of a single-rod type EHA (electro-hydrostatic actuator) in the closed-loop control of piston position is inherently dependent on load directions due to the unequal piston areas of the rod-side and head-side. In particular, the response time of the extension and retraction of the piston rod changes significantly when the direction of the external load is changed. In this study, a dual EHA system is proposed, where a force-controlled double-rod type EHA was added to a single-rod type EHA to isolate it from external loads. Force signals for the force control were obtained by measuring the cylinder chamber pressures. The dual EHA system exhibited significantly improved position control performance, even when using basic proportional controllers. An expected collateral benefit is that the system may be reconfigured to a redundant system for fail-safe operation in the emergency case where the main position controlled EHA is malfunctioning.

Model-based force and position tracking control of an asymmetric cylinder with a digital hydraulic valve

AbstractThis paper presents a model-based control solution for large inertia systems controlled by a fast digital hydraulic valve. The solution is based on model-based force control and it is shown that the cylinder chamber pressures have first order dynamics with the proper parameter selection. The robust stability is analyzed under unknown load mass, bulk modulus, and delay, and it is shown that a simple cascaded P + PID controller results in good control performance and robustness. The simulated results show smooth and stable response with good tracking performance despite large variations in the load mass and bulk modulus.

Vibration and Cylinder Chamber Pressure Characteristics of an Air Reciprocating Compressor

In the application of a reciprocating compressor failures are often caused by valve malfunction. The failure can be minimized by a proper valve design. This research described an experimental study to investigate characteristics of vibration and cylinder chamber pressure diagrams, as results of open-close valve processes in a single-stage, single-acting air reciprocating compressor. Vibration and pressure were measured at the same crank angle. The modification was materialized by a change in a valve seat profile of a discharge side. The study was conducted for several working loads. Compared to the discharge valve which was (commonly) supplied by the manufacturer, the result showed that a provision of a taper angle on a discharge valve seat would decrease vibration level, made longer discharge opening, and would increase discharge pressure.

A hydraulic cylinder model for multibody simulations

In this paper we present a model for a linear hydraulic actuator for multibody simulations. In addition to translational degrees of freedom also the cylinder chamber pressures are taken as state variables. In static analysis the chamber pressures are embedded thus a purely mechanical simulation can be performed. In dynamic analysis we end up to a coupled problem where the chamber pressures are separate variables. The sealing friction is taken into account in both static and dynamic analysis. For numerical solution we use a monolithic algorithm and the coupling matrices between the hydraulic and mechanic variables are presented.

Study on a Type of Pneumatic Force Servo System

A type of pneumatic force servo system is discussed in this paper. In this system, output pressure depends on pressure difference between two chambers of cylinder; by controlling pilot-operated reducing valve will get different cylinder chamber pressure. Dynamic mathematical model and control Strategy of this system is founded in this paper. By mathematical model and control Strategy, the digital simulation results show how system performance with different gas source pressure and rodless cavity size..

마찰력 보상을 고려한 공기압 실린더의 위치제어

The paper describes a technique that compensates a friction in pneumatic cylinder to perform the position control. The friction is one of the most common nonlinearities present in pneumatic actuating systems. For accurate position control and low velocity control, control strategies usually rely on accurate estimation of friction. This paper presents a observer to estimate the friction force in the pneumatic cylinder from the pressures in cylinder chambers. Also, the stiction compensation of a pneumatic cylinder is obtained by adding pulses to the control signal using impulsive control. The characteristics of the pulses in impulsive control are determined from the control action. The simulation results are proved that the method proposed here is effective.

Detection and Isolation of Leakage and Valve Faults in Hydraulic Systems in Varying Loading Conditions, Part 1: Global Sensitivity Analysis

Model-based condition monitoring methods are widely used in condition monitoring. They usually rely on ad hoc approaches to verify the system model and then best practices are reported to detect the given set of faults. This first part of a two-piece paper introduces a generic Global Sensitivity Analysis-based approach that can be applied systematically to verify the model parameter sensitivities used for the model-based fault detection. The case study is a generic servo valve-controlled hydraulic cylinder with unknown loading condition which is then systematically analyzed with Global Sensitivity Analysis. The method shows valuable insight into systematic model verification and resulting fault detection in terms of showing the dominant sensitivity of the nominal flow rate and nominal pressure difference, and the exact sensitivities of 0-1 dm3/min external and internal leakages on cylinder chamber pressures and velocity. In the second paper, an Unscented Kalman Filter-based Fault Detection and Isolation scheme for leakage and valve faults of a generic servo valve-controlled hydraulic cylinder is devised and fault patterns are presented.

양방향 회전형 사축식 유압 피스톤 펌프의 벨브 플레이트 형상이 토크 맥동에 주는 영향

EHA용 유압 펌프의 토크 맥동은 저속 회전 영역에서 실린더 위치의 제어에 외란으로 작용할 수 있다. 원칙적으로 피스톤 펌프에 의해 발생되는 반력 토크의 주기적인 변화는 실린더 압력의 파형과 밀접한 관계를 가지고 있다. 일정 속도로 회전하는 단방향 피스톤 펌프의 경우에는 밸브 플레이트의 예압각이나 노치를 활용하여 실린더 압력의 오버슈트나 변화율을 조절할 수 있다. 따라서 본 연구에서는 밸브 플레이트의 형상이 EHA용 사축식 유압 피스톤 펌프의 토크 맥동에 미치는 영향을 분석하였다. 그 결과로서, 양방향 회전형 유압 피스톤 펌프의 토크 맥동은 회전 속도의 영역에 무관하게 밸브 플레이트의 예압각이나 노치를 이용하여 개선하는 것이 불가능한 것으로 나타났다. The torque ripple of the hydraulic pumps for the Electro-hydrostatic Actuators can disturb the cylinder position control under slewing speed operation condition. In principle, the periodic change of the reaction torque generated by a piston type pump is highly dependent on the waveform of its cylinder chamber pressure. In case of uni-directional pumps operating at constant speed, the transient overshoot and rising slope of the cylinder pressure can be adjusted by the precompression angle and notch shape of their valve plates. Therefore, the influence of the valve plate geometry on the torque ripple magnitude of a bent-axis type piston pump for EHA application was investigated in this study. The results showed that any improvement of the torque ripple of such a bi-directional pump can not be achieved by modifying the valve plate geometry, regardless of its operation speed.

A Nonlinear Observer for Pressure Sensorless Control of Pneumatic Servo System

Pneumatic cylinder servo systems are characterized by high nonlinearities such as the compressibility of air and friction in their sliding parts. An approach to enhancing the control performance of such systems is to construct a pressure feedback control loop in their innermost. However, this requires the acquisition of the pressures in each cylinder chamber, and this acquisition typically depends on the use of costly pressure sensors in practical situations. This paper presents the development of a nonlinear observer to estimate the cylinder chamber pressure from the position sensor output and the valve operating command for replacing these sensors. This observer is designed based on the Lyapunov approach in order to ensure the convergence of the error between the actual and estimated pressures to zero. By incorporating not only designed pressure observers but also a friction observer into a pneumatic servo system for position control, a pressure sensorless control system equipped with only a position sensor is constructed. Experimental results show that this system provides good performance in spite of low cost.

Adaptive Output Force Tracking Control of Hydraulic Cylinders With Applications to Robot Manipulators

An adaptive output force control scheme for hydraulic cylinders is proposed by using direct output force measurement through loadcells. Due to the large and somewhat uncertain piston friction force, cylinder chamber pressure control with Coulomb-viscous friction prediction may not be sufficient enough to achieve a precise output force control. In the proposed approach, the output force error resulting from direct measurement is used not only for feedback control, but also to update the parameters of an appropriate friction model which includes the Coulomb-viscous friction force in sliding motion and the output force dependent friction force in presliding motion. The L2 and L∞ stability is guaranteed for both the pressure force error and the output force error. Under bounded desired output force and its derivative, asymptotic stability of both the pressure force error and the output force error is also guaranteed. The experimental results demonstrate that a good pressure force control system does not necessarily guarantee a good output force control, and that adaptive friction compensation is superior to fixed-parameter friction compensation. The output force control transfer functions of a robot joint driven by two hydraulic cylinders in pull–pull configuration are limited by ±1.5dB up to 20Hz, tested in free motion and in rigid constraint. The excellent output force (joint torque) control performance implies the dynamic equivalency between a hydraulic cylinder and an electrically-driven motor within the prespecified bandwidth. This allows to emulate an electrically-driven robot by a hydraulic robot.

A practical control strategy for servo-pneumatic actuator systems

A practical control strategy with a simple controller structure is proposed for servo-pneumatic cylinder actuator systems. Theoretical analysis reveals that the acceleration of the piston indirectly represents the cylinder chamber pressure difference so it is possible to employ acceleration feedback instead of pressure feedback in the construction of servo-pneumatic actuator control systems. The main features of the control strategy developed in the paper are (1) using acceleration feedback to improve the stability of the system; and (2) introducing time-delay minimisation and optimised null offset compensation to address the problem of time delay and dead zone, which are mainly caused by the compressibility of air and friction. The experimental studies have been conducted using an asymmetric pneumatic cylinder system and the results show that the system performance has been much improved when compared with a conventional PID controller.