Hydraulic Positioning System Research Articles

Research on stability and minimum orifice area of hydraulic servo position control system

This paper reports results of research on the stability of a hydraulic servo position system using generalization pulse code modulation (GPCM) and common on/off valves for hydraulic servo control. The describing function was first used to analyze the system's stability, and based on the nonlinear theory, an equation calculating the minimum orifice area of GPCM valves was derived by applying results of analysis on the stability of the GPCM control system. In the end, aimed at developing a hydraulic servo position system to be used in a paint robot, simulation and experiment were carried out. The results show that the theoretical conclusions accorded with practical results.

Input to Output Linearization with Constrained Measurements

Many practical control applications require nonlinear control concepts to fulfill the high demands on the performance. Often, differential geometric methods, like the well established exact input-to-state or input-to-output linearization approach are not applicable, since the implementation of the feedback law requires the measurement of the whole state. This contribution deals with a refinement of the input-to-output linearization such that the control law depends only on a predefined set of measurements. More precisely, we derive the determining equations for one output function in the single-input, or a set of output functions in the multi-input case, such that the input-to-output map from the new input to the new output is linear and such that the feedback law uses predefined measurements only. Finally, this approach is applied to a hydraulic positioning system.

Nonlinear control in rolling mills: a new perspective

This paper is concerned with the application of modern nonlinear control techniques to the thickness control in rolling mills. It turns out that the performance of the closed loop can be significantly improved by taking into account the essential nonlinearities of the plant to be controlled already in the controller design. These nonlinear control strategies totally differ from the common approach of linearizing the nonlinear system around a nominal operating point, because they are not limited to a more or less small neighborhood of the operating point, but are valid all over the operating range. Practically, these nonlinear control concepts are a possible answer to the trend of modern rolling mills toward tighter thickness tolerances, thinner final strip thicknesses, faster production rates and shorter off-gauge lengths. However, a straightforward application of the well established nonlinear control theory does not always lead to a control concept that is practically feasible. It is rather unavoidable to consider all the special features and properties of the plant. By means of the gap control of a mill stand with a hydraulic positioning system, the authors show in detail the advantages of a nonlinear control approach. Finally, simulation and measurement results demonstrate the feasibility and the excellent performance of the proposed design.

Nonlinear Hydraulic Gap Control: A Practical Approach

This paper presents measurements and evaluates the results of a new nonlinear hydraulic gap controller (HGC) implemented in a reversing hot strip mill. Modern rolling mills contain several feedback loops and the roll gap is usually adjusted by a hydraulic system. Since the HGC is part of the most inner control loop in this cascaded structure, the use of a controller with high dynamics for the hydraulic positioning system is essential due to performance considerations. In order to fulfill the constantly rising demands on the quality as well as on the minimal strip thickness tolerances of the rolled products, it is unavoidable to improve existing control algorithms. Up today, linear design techniques are used for the HGC in most cases, although the nonlinear nature of the hydraulic system can be taken into account by means of modern nonlinear control concepts. Furthermore, the controller must be robust against friction forces, leakage flows, transducer and quantization noise in all possible operating conditions. This paper compares measured step responses of a recently proposed nonlinear controller with conventional linear ones.

Optimal control of hydraulic position system employing high speed On/Off solenoid valve

A hydraulic position system was designed employing two high speed On/Off solenoid valves with PWM(Pulse-width-modulation) technique and using LQ(Linear-Quadratic) optimization principle. Based on the system, the parts of system can be formulated with equations. According to equations, the mathematical model of the system was established. By simulation, the corresponding LQ optimal controller was designed and the PWM signals were generated. The comparison of the simulation and experiment results show that LQ optimal control method with PWM technique employing high speed On/Off solenoid valve can provide better system performance and a high position precision is obtained.

Application of Microcomputer-Based Model Reference Adaptive Control to a Hydraulic Positioning System

Publisher Summary This chapter discusses the application of a microcomputer-based model reference adaptive control to a hydraulic positioning system model. A direct adaptive control scheme based on the model reference principle guarantees stable operation. This is achieved by augmenting the plant output signal using a so called correction network connected in parallel to the plant, which acts as a dynamic weighting filter for the manipulating signal. This network is designed using root locus or pole assignment theory. For parameter estimation, several methods and algorithms such as stochastic approximation and recursive least squares have been employed. Only numerically stable update algorithms such as square-root filtering or UDUT factorization of the covariance matrix are used. The chapter presents some experiments that show that adaptive model reference control assures zero steady-state error for non-negligible load, even in the absence of integral action in the control law.

CJ89-23. Identification of a hydraulic position system and its noise model : By Xiong Yufei and Lu Yuanzhang (Shanghai Jiaotong University, Shanghai, China). Chinese J. Mech. Engng25, No. 2 (June, 1989), pp. 55–60

CJ89-23. Identification of a hydraulic position system and its noise model : By Xiong Yufei and Lu Yuanzhang (Shanghai Jiaotong University, Shanghai, China). Chinese J. Mech. Engng25, No. 2 (June, 1989), pp. 55–60

Frequency Response of an Electro-Hydraulic Vibrator with Inertial Load

During the past few years systematic vibration testing has played an increasing part in the evaluation of mechanical devices. The electro-hydraulic vibrator, consisting of a valve-controlled hydraulic cylinder, is capable of high thrusts over a fairly wide range of frequency. This paper examines the theoretical behaviour of such a vibrator which is itself similar to a hydraulic positioning system. The cylinder equations are extended to include end leakages and the servo valve is examined both for transfer characteristics and the interdependence of flow and load. It is shown that the classical square root relationship between pressure drop and flow does not necessarily apply for a two-stage valve with a spring-centred second stage and that a dimensionless number known as the valve load compensation coefficient describes these characteristics. For practical valves it is possible for the flow to be almost independent of the load over a wide range of operating conditions and thus a linear transfer function can be used for the valve-cylinder combination. The experimental work shows good agreement between the theoretical characteristics and those found in practice.