Hydraulic Servo Control Research Articles

Experimental Investigation on Principal Stress Rotation in Kaolin Clay

A combined axial–torsional testing system was developed to investigate the effect of rotation of principal stresses on the three-dimensional mechanical behavior of Kaolin clay. Uniform and reproducible cohesive specimens having a specimen shape of a hollow cylinder were obtained using a two-stage slurry consolidation technique. Precise stress paths (triaxial compression to pure torsional shear to triaxial extension), corresponding to a fixed rotation of the major principal stress axis, were achieved by using the proportional-integral-derivative (PID) feedback control technique. Kaolin clay specimens were tested under a variety of stress paths associated with a constant principal stress rotation angle (β) under undrained conditions. Typical test results, such as effective friction angle, undrained shear strength, stress–strain relationship, pore pressure evolution, and stress paths are presented as a function of β. During shearing, the procedure to use advanced servo-hydraulic control (using PID algorithm in this study) to maintain a fixed β value that involves updating specimen geometry in real-time is described. A new approach for data analysis and visualization is presented for providing a convenient way of incorporating the effect of major principal stress rotation angle considering the degradation of stiffness as a function of stress path in three dimensions.

Dynamic analysis of variable structure force control of hydraulic actuators via the reaching law approach

This paper describes the design and experimental analysis of a variable structure control (VSC) law using three reaching law strategies for a hydraulic servo control system. For this purpose we use a non-linear mathematical model to develop a stable variable structure force control. The controller is designed using a sliding mode equivalence control and is augmented by a reaching law approach to further improve the performance. Three reaching laws are developed to bring the system states to the sliding mode surface. The feasibility of each reaching law structure on the closed loop performance (i.e. reaching time, chattering and quality of tracking) are experimentally evaluated and analysed.

ニューラルネットと微小振動重畳による不感帯を有する油圧モータ角度制御の特性改善

It is generally not easy to acquire high positioning accuracy in hydraulic servo control systems, since they have an intense non-linearity, such as a dead zone, which is originally caused by leakage and friction. It is considered that the Neural Network compensator is one of the available options to get over the inherent problem. This paper deals with the effect of dither/PWM signals on the steady position error in the hydraulic motor drive system with a state feedback Neural Network. From the computer simulation and the experiment, it is clarified that the application of the dither/PWM signals to the Neural Network control system improves the positioning performance by accompanying the assistance of the Neural Network capability.

Comparison of pullout strength of small-diameter cannulated and solid-core screws

The purpose of this study was to determine the difference in pullout strength between cannulated and solid-core small-diameter bone screws. Cannulated screws from different manufacturers were compared against solid-core screws with 2.0-mm, 2.4-/2.5-mm, and 3.0-mm diameters. A synthetic material made to simulate bicortical bone was used as the test medium. The screws were extracted under servohydraulic control. There was no statistically significant difference between any of the cannulated and solid-core 2.0-mm screws used in this study ( P < .05). In the 2.4-/2.5-mm screw tests, both of the cannulated screw designs had a significantly higher pullout strength when compared with the solid-core screw ( P < .05). In the testing of 3.0-mm screw test, 1 of the cannulated screw designs showed a significantly higher pullout strength than the other cannulated and solid-core screws that were tested ( P < .05). The results of this study suggest that small-diameter cannulated bone screws are similar in mechanical pullout strength to solid-core screws.

Comparison of two inference methods for P-type fuzzy logic control through experimental investigation using a hydraulic manipulator

This paper presents a comparison of the two important inference schemes: “individual-rule-based inference” and “compositional rule of inference” as applied to fuzzy logic control, through experimental investigation. The techniques are implemented on a hydraulic manipulator of an industrial machine with P-type fuzzy control. The fuzzy logic controller is designed for automatic positioning of the cutter blade of an automated fish-cutting machine. The features of the machine, which uses hydraulic servo control for cutter positioning, are outlined. The performance of the machine under the two inference schemes is examined and contrasted. Some practical implementations of the results are indicated.

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.

Experimental Based Analysis of the Pressure Control Characteristics of an Oil Hydraulic Three-Way On/Off Solenoid Valve Controlled by PWM Signal

Pressure control characteristics of a three-way high-speed on/off oil hydraulic solenoid valve driven by a PWM signal with a fixed pulse period were theoretically and experimentally analyzed and evaluated. By virtue of its relatively low cost, small size, robustness to contamination, and simplicity of the driving circuit, the three-way on/off solenoid valve is increasingly and widely used for hydraulic pressure or position control applications. In this paper, two formulas are newly derived for the mean and the ripple amplitude of the system pressure that oscillates with the same frequency as that of the PWM driving signal. The formulas indicate that the mean pressure and the pressure ripple amplitude depend on three major system variables that are the on- and the off-times of the valve and a parameter, the system configuration coefficient a, that characterizes the overall feature of the system. The mean pressure and the ripple are then shown to depend on both the duty ratio and the carrier frequency of the PWM driving signal, which disproves Tanaka’s claim that a single variable is enough to describe two quantities. Several aspects of the formulas are discussed. The accuracy of the new formulas is verified by comparing the calculation results to corresponding experimental test results. A method is proposed to obtain the system parameters of the opening and closing-case delay times, the time constants of the valve and a. The selection criteria are established for the major design parameters of the driving signal, i.e., the duty ratio and the carrier pulse frequency, and a basic strategy is proposed on how to suppress the undesirable ripple for a hydraulic servo control system using three-way on/off solenoid valve.

Adaptive sliding mode tracking control of hydraulic servosystems with unknown non-linear friction and modelling error

This paper deals with the use of adaptive discrete-time sliding mode tracking control in order to assure good tracking performance as well as to guarantee robustness against non-linear frictional forces and modelling error. The control scheme ensures that the absolute value of the sliding function decreases when it is outside the sliding boundary layer and the steady state value of the sliding function is bounded by the sliding boundary layer. Application of the scheme to a hydraulic servosystem has shown that adaptively estimated frictional forces compare favourably with those obtained from direct measurement. A significant reduction in tracking error is achieved through the use of non-linear friction compensation.

Frequency Domain Modelling and Identification of 2D Digital Servo Valve

The 2D digital servo valve studied here is a two-stage valve designed by using both rotary (angular) and linear motions of a spool. The rotary motion is driven by a stepper motor operating under continual angular displacement control, while the linear motion of the spool is actuated by hydraulic servo control with feedback of the spool's displacement, which is achieved by a unique “servo screw”.The modelling of the 2D valve is based on linear theory and is further verified by the special experiments. Because of the extremely large hydraulic natural frequency, the control of the 2D valve is identified as being that of a first-order-system. The relation between the time constant and the structural parameters is established, accounting for the non-linearity of the pilot hydraulic bridge. For the continual control of the stepper motor, a mathematical model considering the rotary motion, the rotating magnetic field and the angular control signal is established. In order to prevent the stepper motor from losing steps, the rate of the control signal is limited to a certain range. As a result, this may cause a non-linearity and, consequently, the deformation of the waveform when the input sinusoid wave is of large amplitude and high frequency. By utilizing the method of the description function, the effect of limiting the rate of the control signal is approximated as a first-order-system and the relation between the time constant and the amplitude and frequency is presented. The dynamic characteristics of the stepper motor are to a large extent dependent upon the way the power is supplied. For a constant current supply, the stepper motor can be classified as a second-order-system. The factors affecting the natural frequency and damping ratio are clarified. Finally, the frequency response of the 2D digital valve is experimentally measured and compared with theoretical results. Both theoretical and experimental results show that the 2D digital valve has a fairly high frequency response, especially when the valve operates near the central position. For a 25% full scale input signal, the 2D digital servo valve has at least 300 Hz under the gain of–3 dB.

Neural networks and hydraulic control—from simple to complex applications

The control of hydraulic servo-systems has been the focus of intense research over the past decades. The highly non-linear behaviour of these devices makes them ideal subjects for applying different types of sophisticated controllers. This paper considers the application of neural networks to the control of hydraulic servo-systems subjected to either non-linear friction or highly coupled loads. Three applications are considered: a very simple quasi-open-loop pattern follower, a proportional-integral-derivative (PID) multiple-gain neural controller and a neural-based controller for a very complex multiple-input multiple-output system. A major factor in these applications is the fact that the neural network controllers have been applied to real-time control of experimental systems. In all cases, these controllers showed superior performance over conventional-type PID controllers.

Experimental and Theoretical Study of the Static and Dynamic Behavior of a Variable-Displacement Pump with Power Control

This paper deals with the static and dynamic behavior of a variable displacement bent axis axial piston pump with power controller. A mathematical model is deduced to predict the performance of the studied pump and its hydraulic servo controller. The developed model, which takes into consideration the basic pump and controller nonlinearities is used to develop a computer simulation program for the pump. The steady state flow-pressure characteristics and pump transient response are predicted by using the simulation program. The pump static and dynamic characteristics are also measured. The study showed good agreement between theoretical and experimental results. The study provides good foundation for the future work aiming at improving the pump performance by finding out optimum constructional parameters.

Pressure control of hydraulic servo system using proportional control valve

The purpose of this study is to develope a control scheme for the hydraulic servo system which can rapidly control the pressure in a hydraulic cylinder with very short stroke. Compared with the negligible stroke of the cylinder in the system, the flow gain of the proportional pressure control valve constituting the hydraulic servo system is relatively large and the time delay on the response of the valve is quite long. Therefore, the pressure control system, in this study tends to get unstable during operations. Considering the above mentioned characteristics of the system, a two-degree-of-freedom control scheme, composed of the I-PDD2… feedback compensator and the feedforward controller, is proposed. The reference model scheme is used in deciding the parameters of the controllers. The validity of the proposed control scheme is confirmed through the experiments.

Strain rate change transients during cyclic deformation of copper

In the present study, the authors have undertaken to apply the strain rate change method to mechanically probe the mechanisms of cyclic deformation in copper. The goals of this work were twofold: to carefully explore differences in results obtained under conventional displacement control with those recorded under plastic strain control and to apply the formalism for monotonic deformation described above to cyclic deformation. To achieve these goals, it has been necessary to utilize computed-variable servo-hydraulic control to develop a new test technique incorporating strain rate change tests performed during low cycle fatigue. Plastic strain is used as the control variable to ensure a constant plastic strain rate between pre-determined plastic strain limits.

Development of Water Hydraulic Servo Control System Considering Water Characteristics.

The oil hydraulic servo control system has a long history of application to various machines. However, a cleaner hydraulic fluid is necessary as we are faced with problems of fire or contamination due to oil leakage. We succeeded in improving the performance of a water hydraulic servo control syrstem over that of the oil hydraulic servo control system. Our water hydraulic servo control system is based on the analysis of the advantages of the physical properties of water for servo control. Furthermore, we can fabricate a simple water servo control system consisting of least components which can cover a wide dynamic performance range and can guarantee the same applications fields as the oil hydraulic servo control systems. Important components are the wide-dynamic-range water hydraulic pump system and the high-response, wide-dynamic-range water servo valve. The performance and durability of the system and components were tested and verified. As a result, the water hydraulic servo control systems are found to be the same as or superior to the oil hydraulic servo control system. Applying the advantages of the properties of water to a design, we can achieve better performance and lower cost with the water hydraulic servo control system than the conventional oil hydraulic servro control systems.

Capsular restraints to anterior-posterior motion of the abducted shoulder: A biomechanical study

Twenty-three fresh-frozen cadaver shoulders free of degenerative arthritis or rotator cuff disease were tested biomechanically to quantitate the contribution of specific capsular structures to restricting anterior-posterior translation of the abducted shoulder. With the glenohumeral joint in 90 degrees of abduction on a servohydraulic control testing system, translation was measured in 30 degrees of forward flexion (with regard to the coronal plane of the scapula), 0 degree, and 30 degrees of extension while a 25 N anterior-posterior load was applied. Measurements were taken both in the intact (vented) shoulder and after selective cutting of different capsuloligamentous structures was performed. In the intact shoulder the largest anterior-posterior translation occurred in 0 degree of horizontal flexion and extension with regard to the scapular plane, with equal amounts of anterior and posterior translation noted. The primary anterior-posterior stabilizer of the abducted shoulder is the inferior glenohumeral ligament complex. The anterior band is the primary stabilizer in 30 degrees of horizontal extension and at 0 degree (neutral). The posterior band is the primary stabilizer in 30 degrees of horizontal flexion. This study quantifies for the first time the normal amount of anterior-posterior translation in the intact cadaveric shoulder model. In addition, it demonstrates the relative role of the anterior and posterior band of the inferior glenohumeral ligament complex in stabilizing the glenohumeral joint at 90 degrees of abduction, where most clinical instability of the shoulder occurs.

Application of an Adaptive Model Following Control Technique to a Hydraulic Servo System Subjected to Unknown Disturbances

This paper deals with a position control of hydraulic servo systems subjected to unknown and time-varying external load disturbances. Since hydraulically operated processes are often subjected to unknown disturbances, an adaptive model following control (AMFC) scheme was derived based upon the Liapunov’s Direct Methods which was employed by Monopoli (1981). As an adaptation criterion this method utilizes an ultimate boundary of the uncertain parameters associated with the plant dynamics and the unknown disturbances. The performance of the derived adaptive controller is evaluated through simulation and experimental studies. The results show that the proposed AMFC is fairly insensitive to unknown and time-varying external load disturbances, yielding much better response characteristics, compared with those of a conventional constant PI feedback controller.

A system for automatically testing properties

A test system was developed at Caterpillar to automatically measure the static stiffness as well as complex stiffness and phase angle of rubber mounts used for support, and for noise and vibration isolation in our vehicles. The system consists of a load frame with a hydraulic cylinder that applies load to the mount and an instrumentation and control system interconnected with a personal computer. The computer acquires load and displacement measurements from the mount through an analog-to-digital converter connected to computer controllable signal conditioners. The computer acts on these signals and controls a programmable function generator, which supplies a command signal to a hydraulic servo controller that controls load or displacement of the mount. The test system software allows the operator to configure the test through form fill-in menus and special function keys. Following setup, the system automatically runs the tests and prints or plots results to the CRT and optionally to the system printer. Additionally, the system allows the operator to specify characteristics of the sensors being used and guides the operator through calibration of the signal conditioners.

Hard tissue lubrication by salivary fluids

The frictional coefficients for human parotid (HPS) and human submandibular/sublingual (HSMSL) salivas and water were measured for five subjects. Twenty different biomechanical conditions were used which approximated the range of force and movement of the human mandible. The experimental set-up comprised a bruxing motion under servohydraulic control; a microchamber with a small recirculating volume (3 ml minimum) under physiologic temperature control; and a maxillary element capable of measuring frictional forces at the enamel interface. The relative movement of enamel-on-enamel demonstrated the slip-stick phenomenon which was consistent with the negative velocity gradient of the coefficient of friction under all conditions. Studies on the variation of the frictional forces as a function of vertical load confirmed that the mechanism of lubrication was thin film, under the experimental conditions. HSMSL saliva had the greatest potential to vary the lubrication mechanism. At low speeds and higher force, it is suggested that boundary lubrication may offer the greatest potential in the development of enhanced lubrication of the hard tissues in the oral cavity.

Hydraulic servo control spool valve : Donal Miller assigned to Battelle Memorial Institute

This paper presents the idea of linkage path code for the identification and recognition of planar kinematic chains with simple joints and turning pairs. For every given chain, this code can be obtained according to the definition directly or by a proposed method which can greatly simplify the procedures for obtaining the code by inspection.

A high-strain biaxial-testing rig for thin-walled tubes under axial load and pressure

It is well know that high-strain biaxial testing with axial force and pressure on thin-walled tubes can be interesting from several points of view: capability of testing over the whole range of strain or stress ratios, great versatility of testing. and because of the physical system, the measured strains and stresses are principal. Nevertheless, there are few experimental-biaxial-fatique data due to the complexity of the testing equipment involved. In this paper, an experimental testing rig capable of subjecting thin-walled tubes to combined dynamic loadings in tension-compression with torsion and tension-compression with internal-external pressure is presented. The following components are described: the mechanical and hydraulic system, servohydraulic control, specimen configuration, strain-measuring equipment and data-acquisition system. The computation of stresses and strains, as well as examples of data acquisition, are also shown.