Servo-hydraulic Actuator Research Articles

Hardware-in-the-Loop Simulation for Compound Catenary Systems

This study proposes a new pantograph testing method for railway pantograph/overhead contact lines (OCL) systems, based on hardware-in-the-loop simulation (HILS) consisting of a physical pantograph and a numerical compound OCL model. A servo-hydraulic actuator fixed to a frame structure is used to realize vertical displacement of the contact wire model. In order to compensate for phase lag of the servo-hydraulic actuator and stabilize the HILS system, the dynamically substructured system (DSS) method is used. This HILS enables the investigation of dynamic interactions between the contact wire of the OCL and the pantograph head, due to dropper-passing of the pantograph. In order to validate the proposed method, HILS testing is carried out at the Railway Technical Research Institute. The contact force between the actuator and the pantograph head is measured using a loadcell. Results from this experimental investigation are compared with those generated by a numerical simulation of the emulated system, i.e. the system to be represented by the HILS experimentation.

Motion synchronization for the SHA/EMA hybrid actuation system by using an optimization algorithm

The current research develops a mathematical model and control strategies to address two major problems force fighting and precise position tracking for a hybrid actuation system composed of servo-hydraulic actuator and electro-mechanical actuator (SHA/EMA). The force fighting and desired position tracking are two essential problems of the SHA/EMA actuation system for a large civil aircraft. The trajectory-based fractional order proportional integral derivative (FOPID) control for the SHA/EMA actuation system is proposed, tuned with the help of the particle swarm optimization (PSO) technique and implemented with the support of the FOMCON toolbox in Matlab. The experiments are performed under different external aerodynamic loads that the aircraft usually experiences during flight operations. The results show that the proposed method shows better results for tracking performance, force fighting and load rejection ability.

System Performance Analysis for Trimmable Horizontal Stabilizer Actuator Focusing on Nonlinear Effects: Based on Incremental Modelling and Parameter Identification Methodology.

With the development of more/all electric aircraft, replacement of the traditional hydraulic servo actuator (HSA) with an electromechanical actuator (EMA) is becoming increasingly attractive in the aerospace field. This paper takes an EMA for a trimmable horizontal stabilizer as an example and focuses on how to establish a system model with an appropriate level of complexity to support the model-based system engineering (MBSE) approach. To distinguish the nonlinear effects that dominate the required system performance, an incremental approach is proposed to progressively introduce individual nonlinear effects into models with different complexity levels. Considering the special design and working principle of the mechanical power transmission function for this actuator, the nonlinear dynamics, including friction and backlash from the no-back mechanism, and the nonlinear compliance effect from the mechanical load path are mainly taken into consideration. The modelling principles for each effect are addressed in detail and the parameter identification method is utilized to model these nonlinear effects realistically. Finally, the responses from each model and experimental results are compared to analyze and verify how each individual nonlinearity affects the system’s performance.

Development of Generic Frame Testing Methodology by Synthetic Drive File Generation Technique

<div class="section abstract"><div class="htmlview paragraph">Frame is one of the vital part of Light & Heavy Commercial vehicle which holds all the parts and testing the frame is not a cost effective as the complete vehicle assembly needs to be tested as the individual testing of frame is not formulated for testing. In the development stage of the vehicle we always seek for a quick, cost effective and reliable methodology so that any modification can be made by identifying the failures. In this paper we have addressed this problem by developing a generic frame test methodology by which the frame can be tested in the preliminary stage of development in a cost effective way and reliable way. The Multi Body Dynamics Simulation was carried out and rig was designed comprising of servo hydraulic actuators. The frame was instrumented to acquire the Field, Event and Torture track data for the formulation and verification of the synthetic drives. Instead of Random Vibration Simulation for the frame simplified events of the bending, oblique bending, and torsion were formulated in the form of Synthetic Drives. These drives were generic and applicable to any frame of the similar category also it can be amplified as per the requirement. Synthetic Drive were generated for a Light Commercial Vehicle (LCV) from an OEM. The Synthetic Drives were tested in Automotive Research Association of India (ARAI) - Structural Dynamics Lab (SDL) and verified. The Rig Setup and Synthetic Drive Developed showed a good correlation in terms of damage correlation and rig response and a promising & successful step towards Generic Frame Testing for Light & Heavy Commercial Vehicle Frame.</div></div>

Modelling and transient response study of hydraulic servo actuator

This paper presents a mathematical model of electro hydraulic servo system (EHS) using two-stage electrohydraulic servovalve (EHSV), by the aim of Matlab-simulink-simscape multibody to predict the flow characteristics (pressure/flow rate) with changing the parametric configuration of (EHSV), these parameters could be used to estimate the error at different operating conditions. It includes establishing mathematical model, controller model and validating the performance of the (EHSV) by experimental result of published work using the data of servovalve labelled B.31.210.12.1000.U2V (mechanical feedback) manufactured by PPT - Trstenik. The effect of changing servovalve orifice diameter (0.25, 0.30, and 0.35) mm, show that increasing the orifice diameter of the servovalve leads to increase the transient time but decrease the system overshoot. The pressure behaviour is plotted and shows that increasing the orifice diameter leads to increasing the pressure inside the system as to reach the relieve pressure.

Mechanical response of full-scale geosynthetic-reinforced asphalt overlays subjected to repeated loads

This study aims at evaluating the influence of geosynthetic reinforcements on the structural improvement of asphalt overlays placed on distressed pavement layers using repeated load tests. Full-scale instrumented pavement models were constructed in an indoor steel tank measuring 1000 mm in length, 1000 mm in width and 1000 mm in depth. Full-scale instrumented pavement models consisted of a 650-mm-thick weak subgrade, 250-mm-thick base, 90-mm-thick distressed asphalt layer, binder tack coat, geosynthetic reinforcement (except in control sections), and 50-mm-thick hot mix asphalt overlay. Sensors used in the instrumentation program included earth pressure cells and linear variable displacement transformers installed on the subgrade and surface layers, respectively. Four different geosynthetic types, including woven geo-jute mat (GJ), polypropylene geogrid (PP), polyester geogrid (PET), and fiberglass geogrid composite (FGC) were adopted as asphalt reinforcements. A servo-hydraulic actuator was used to replicate a live traffic wheel load by applying an equivalent single axle contact pressure of 550 kPa at a frequency of 1 Hz. Repeated load tests were terminated after 100,000 load cycles and the behaviour of geosynthetic-reinforced full-scale models was compared with that of unreinforced model. Performance indicators, including Traffic Benefit Ratio (TBR) and Rut Depth Reductions (RDR), were estimated and repeated load test results indicated an increase in the structural performance of geosynthetic-reinforced full-scale models in relation to that of unreinforced model. Among the geosynthetic-reinforced models considered in this study, the FGC-reinforced model showed a comparatively better performance with a maximum TBR of 20 at a permanent deflection of 5 mm and the highest RDR of 56% after 100,000 load cycles, respectively. Maximum reductions of 56% in surface deflection and of 30% in vertical pressure on the subgrade were also observed after 100,000 load cycles in the FGC-reinforced model.

Probabilistic Analysis of a Linearized Servo-Hydraulic Model for Real-Time Structural Testing

ABSTRACT Servo-hydraulic actuators are often used in real-time hybrid simulation to impose desired displacements to specimens and to maintain the boundary compatibility between substructures. Previous studies often consider the servo-hydraulic system as deterministic while experimental results indicate otherwise due to different sources of uncertainties. This study utilizes the generalized likelihood uncertainty estimation method to explore the uncertainties in servo-hydraulic dynamics. Probabilistic distribution and statistical moments are derived for parameters of a linearized servo-hydraulic model based on experimental results. The analysis results are further applied to demonstrate the effects of servo-hydraulic uncertainties on actuator tracking and compared with the corresponding deterministic model.

Mixed Sensitivity-Based Robust H∞ Control Method for Real-Time Hybrid Simulation

Real-time hybrid simulation (RTHS), dividing the emulated structure into numerical substructures (NS) and physical substructures (PS), is a powerful technique to obtain responses and then to assess the seismic performance of civil engineering structures. A transfer system, a servo-hydraulic actuator or shaking table, is used to apply boundary conditions between the two substructures. However, the servo-hydraulic actuator is inherently a complex system with nonlinearities and may introduce time delays into the RTHS, which will decrease the accuracy and stability of the RTHS. Moreover, there are various uncertainties in RTHS. An accurate and robust actuator control strategy is necessary to guarantee reliable simulation results. Therefore, a mixed sensitivity-based H∞ control method was proposed for RTHS. In H∞ control, the dynamics and robustness of the closed-loop transfer system are realized by performance weighting functions. A form of weighting function was given considering the requirement in RTHS. The influence of the weighting functions on the dynamics was investigated. Numerical simulations and actual RTHSs were carried out under symmetric and asymmetric dynamic loads, namely sinusoidal and earthquake excitation, respectively. Results indicated that the H∞ control method used for RTHS is feasible, and it exhibits an excellent tracking performance and robustness.

No Significant Difference Between Intramedullary and Extramedullary Button Fixation for Distal Biceps Brachii Tendon Rupture After Cyclic Loading in a Cadaver Model

PurposeTo biomechanically compare intramedullary (IM) versus extramedullary (EM) distal biceps button fixation under cyclic loading conditions, which is most representative of postoperative physiologic status.MethodsThis controlled laboratory study used 13 fresh-frozen matched paired cadaver elbows. One specimen from each pair was randomized to either IM (unicortical) or EM (bicortical) distal biceps button fixation via onlay technique. A servohydraulic actuator was used to cycle each specimen from full extension to 90° of flexion at 0.5 Hz for 3,000 cycles. All specimens were subsequently loaded to failure to simulate an acute postoperative load.ResultsDuring cyclic loading, the mean change in force from cycle 5 to cycle 3000 was 2.1 ± 3.2 N for the IM group and 0.6 ± 4.2 N for the EM group (P = .19). The increase in tendon gap for the IM group was 1.02 mm and for the EM group was 1.83 mm (P = .37). During failure loading, the IM group had a mean failure load of 154.9 ± 44.5 N and the EM group a mean failure load of 191.1 ± 62.6 N (P = .16).ConclusionsNo significant differences exist between the IM and EM techniques in loss of force and tendon gap formation under cyclic loading or load to failure conditions. Thus, IM fixation may adequately facilitate optimal bone-tendon apposition, with less risk of iatrogenic injury to the posterior interosseous nerve that can be seen with bicortical extramedullary fixation.Clinical RelevanceThe most common major complication following distal biceps repair is PIN palsy. IM fixation may be sufficient in facilitating optimal bone-tendon apposition and healing with onlay technique, while minimizing risk of iatrogenic PIN injury associated with EM fixation.

Shaking table control via real-time inversion of hydraulic servoactuator linear state-space model

In this work, a Model-Based Control method for a single horizontal degree of freedom shaking table is presented. The proposed approach relies on the real-time inversion of a previously identified linear state-space model of the hydraulic servoactuator which drives the table. The inputs to the model are the control command and the force exerted on servoactuator rod. The latter contains all the relevant information related to the external actions acting on the servoactuator, thus making control system performance independent from the specimen with which the table is loaded and enabling it to cope with specimen non-linear behavior and eventual external forces exerted on it. A parallel proportional integral derivative controller, which accounts for non-modeled dynamics and a feedback linearization scheme, aimed at minimizing servovalve flow non-linearity, complement the previous architecture. The effectiveness of the method has been assessed numerically. According to the simulation results, the performance of the proposed technique appears quite promising; however, several factors must be carefully considered to achieve successful actual implementation.

Multiple-input and multiple-output force control for automobile component road simulation using model predictive control with proportional–integral–derivative

When developing an entire vehicle system, testing the structure of the vehicle or each component as a module or individually is necessary to determine the reliability and ensure the endurance of the entire vehicle. Various tests have been conducted to check the durability of the parts. However, the most important part is the verification of the fatigue limit of the load vibration from the road surface when the vehicle is being driven. Verification can be achieved by experimenting while driving on a real road with a prototype vehicle best suited to the actual conditions. However, issues such as problems in time, space, and environmental constraints, inconsistency in driving characteristics of the test driver, and continuous monitoring exist. For testing the load vibration of the road surface in automobile parts in the laboratory, hydraulic servo actuators are used because they provide vibrational loads in multiple directions by configuring them in multiple axes rather than a single axis. In this article, a multiple-input multiple-output model predictive control–proportional–integral–derivative hybrid controller is proposed as the method for optimal control of a multi-axis hydraulic servo actuator used in a random road signal reproduction experiment. Its performance is compared with the simple proportional–integral–derivative controller. A method for obtaining an efficient black box multiple-input multiple-output system model using LabVIEW in a laboratory in the field is also introduced, and the effectiveness of the model predictive control–proportional–integral–derivative hybrid controller is shown by reproducing the actual road load.

Integral Nonsingular Terminal Sliding Mode Control of Hydraulic Servo Actuator Based on Extended State Observer

Hydraulic servo actuator always suffers from various disturbance and uncertainties, which makes it difficult to design a higher performance controller. In this paper, an integral nonsingular terminal sliding mode controller based on extended state observer (ESO‐INTSM) is proposed to improve the robust performance of hydraulic servo actuator. The ESO is designed to estimate not only the parametric uncertainties but also the model disturbance. Based on the observed states of ESO, the proposed controllers could enable hydraulic servo actuator to track the desired motion trajectories. The stability of the synthesized controller is proved via Lyapunov analysis, which is very important for high‐accuracy tracking control of hydraulic servo actuator. Simulation and experimental results demonstrate that the proposed control strategy can effectively attenuate the adverse influence caused by the uncertainties and apparently improve the tracking accuracy.

A Shake Table Frequency-Time Control Method Based on Inverse Model Identification and Servoactuator Feedback-Linearization

Shake tables are one of the most widespread means to perform vibration testing due to their ability to capture structural dynamic behavior. The shake table acceleration control problem represents a challenging task due to the inherent non-linearities associated to hydraulic servoactuators, their low hydraulic resonance frequencies and the high frequency content of the target signals, among other factors. In this work, a new shake table control method is presented. The procedure relies on identifying the Frequency Response Function between the time derivative of pressure force exerted on the actuator’s piston rod and the resultant acceleration at the control point. Then, the Impedance Function is calculated, and the required pressure force time variation is estimated by multiplying the impedance by the target acceleration profile in frequency domain. The pressure force time derivative profile can be directly imposed on an actuator’s piston by means of a feedback linearization scheme, which approximately cancels out the actuator’s non-linearities leaving only those related to structure under test present in the control loop. The previous architecture is completed with a parallel Three Variable Controller to deal with disturbances. The effectiveness of the proposed method is demonstrated via simulations carried over a non-linear model of a one degree of freedom shake table, both in electrical noise free and contaminated scenarios. Numerical experiments results show an accurate tracking of the target acceleration profile and better performance than traditional control approaches, thus confirming the potential of the proposed method for its implementation in actual systems.

A Study on Failure Analysis and High Performance of Hydraulic Servo Actuator

Hydraulic servo actuator is used as the core actuator in tensile compression fatigue life test equipment as it operates the micro displacement very precisely at a high frequency and can be used continuously for a long period of time. Recently, the life expectancy of automobiles has been extended, the load conditions of accelerated life testing on auto parts have been increased, and the life test time and number of tests have increased significantly in order to secure the reliability of the guaranteed life of produced vehicles. Therefore, hydraulic servo actuators mounted on accelerated life testing equipment for automotive parts are essential for much higher performance and a longer life than those tested. However, small- and medium-sized companies that supply test equipment for the fatigue life of auto often fail to develop technology due to a lack of research personnel and the development budget compared to the capabilities of large automobile manufacturers, resulting in frequent breakdowns due to the technical overload of test equipment. In this study, servo actuators were used to test automotive parts, with a maximum output of 2 ton, a maximum frequency of 3.3 Hz and a maximum displacement of 50 mm. The hydraulic servo actuator, which was installed in the tensile compression fatigue life test equipment, failed to operate normally at the site, and by analyzing it, we realized this resulted from the heat generation of insulation compression due to the accumulation of air and gas into the hydraulic oil and the increase in friction due to the deterioration of flow. A static pressure bearing was adopted as a design change to improve the root cause for this failure mode, and a very high level of geometric concentricity was secured by inserting concentric tubes outside the labyrinth seal type piston. The newly designed and manufactured actuator is the result of research that has achieved a semi-permanent long life and improved performance up to 100 Hz by non-contact operation.

Influence of Specimen Geometry on the Response of Post-Installed Anchors Subjected to Constant Load under Crack Opening and Crack Cycles

Abstract It is generally acknowledged that one of the most critical tests to capture the behavior of a post-installed fastener under seismic action is the so-called “seismic crack movement test,” which consists in applying a constant load to a single fastener installed in a crack subjected to opening and full closing cycles. This article presents experimental results of crack movement tests on large size post-installed anchors that show a strong influence of the geometry of the concrete specimen in which the anchor is installed. To improve the regularity of the crack plane, a feedback control using the crack opening signal is applied to the servo-hydraulic actuators. Results of seismic crack movement tests using two different test setups were compared. The major aspects are as follows: (i) splitting force generated by the anchor affects the restoring of the zero crack opening when increasing the number of cycles, and (ii) increasing the size of concrete element limits the effects of bending induced in the concrete specimen. The issue of residual crack opening at the zero actuator’s load is observed experimentally and is further approached both analytically and numerically. The parameters that mostly affect the crack closure phase, i.e., steel ratio, transfer length, and de-bonding length, are finally discussed.

Experimental study on ultra-high performance concrete under triaxial compression

Ultra-high strength concrete (UHSC) and Ultra-high performance concrete (UHPC) with high compressive strength and good durability have been increasingly used in engineering structures. In the present study, uniaxial and triaxial compression tests on UHSC and UHPC are carried out by using servo-hydraulic actuators to investigate the mechanical properties of UHSC and UHPC under various stress states. In triaxial compression tests, the confining pressure ranging from 0 to 50 MPa is applied on UHSC and UHPC specimens. The mechanical responses of UHSC and UHPC specimens under various confining pressures, including peak strength, axial and circumferential strain are recorded in the loading process. According to the elastoplastic behavior of UHSC and UHPC specimens in tests, the influence of confining pressure on the compressive strength and plastic deformation performances of UHSC and UHPC are studied. It is found that the compressive strength and plastic deformation capacity of UHSC and UHPC tend to be higher with the increasing of confining pressure. The enhancement of compressive strength of UHPC is slightly lower than that of UHSC However, due to the lateral restraint effect of the confining pressure and the tensile action of the steel fibers inside the UHPC specimen, failure of the cylindrical specimen are delayed more significantly with increasing of confining pressure. Failure surfaces based on Ottosen’s criterion for UHSC and UHPC are identified accroding to test data. By comparing and analyzing the tests results on UHSC, UHPC and previously tested C200, it is concluded the effect of confining pressure on the enhancement of compressive strength of concretes has a negative relationship with the uniaxial compressive strength of concretes.

Experimental investigation of a ballastless asphalt track mockup under vertical loads

This study presents experimental results from a laboratory investigation into the mechanical behaviour of a ballastless asphalt track under vertical loads and isothermal conditions. A full-scale test section was constructed inside a steel box, consisting of three wide-base sleepers resting on an asphalt layer that was underlain by an unbound granular layer (UGL) supported on a rubber mat (representing subbase and subgrade). Sensors were installed to measure diverse responses, consisting of vertical stresses at the bottom of the UGL, horizontal strains at the bottom of the asphalt layer, relative vertical displacements between various track components, and vertical surface accelerations. Sleepers were loaded directly on top of the rail pads by using servo-hydraulic actuators. Cyclic loads were applied to investigate the effects of different excitation amplitudes and frequencies. It was found that all measured responses displayed a strong frequency dependence. Vertical stresses below the UGL varied linearly with the load amplitude, while other responses showed a non-linear relationship. Train passages with a maximum speed of 200 km/h and axle loads up to 200 kN were simulated by sequentially loading the three sleepers. From this load type, it was found that ballastless asphalt track exhibited time-dependent behaviour such as delayed recovery of strains in-between axle passes. Furthermore, the majority of the vertical actuator displacement was absorbed by rail pad compression. Lastly, measured stresses and strains were of very low magnitudes, suggesting marginal long term mechanical damage under service loads for such a ballastless asphalt track structure.

Behavior of high-performance concrete under multiaxial tensile-compressive loading

In this study, an experimental investigation was conducted to determine the triaxial tensile-compressive-compressive (T–C–C) behavior of three different high-performance concrete (HPC) groups with uniaxial compressive strength ranging from 44 to 90 MPa, using servo-hydraulic actuators. In the experimental program, seventeen stress ratios for each batch of HPC were designed, ultimate strength, principal stress–strain curves under T–C–C were measured and recorded, as well as crack patterns. The test results revealed that the uniaxial compressive strength and the stress ratios had a negative effect on the normalized ultimate strength and deformation of HPCs under T–C–C loading. An increase in the minimum principal stress (tensile stress) significantly decreased the ultimate strength, stiffness, and ductility of the HPC samples. Compared with the minimum principal stress effect, intermediate principal stress effect is not obvious for HPCs at different stress ratios. With increasing uniaxial compressive strength, the obtained normalized ultimate strength and deformability of HPCs decrease. Tensile brittle failure mode was observed for the HPC samples under triaxial T–C–C loading. Finally, a modified four-parameter failure criterion was established for HPC based on the experimental results, regarding the effect of uniaxial compressive strength.

Attempting AG-Doped Diamond-Like Carbon Film to Improve Seal Performance of Hydraulic Servo-Actuator.

A hydraulic servo-actuator is a critical aircraft control device whose sealing performance directly affects the sensitivity and accuracy of the aircraft flight attitude. Foreign intrusive particles in hydraulic oil may induce the vulnerable friction pair wear and the seal leak; they may even lead to oil spill accidents. This work attempts to conduct a systematical investigation of Ag-doped diamond-like carbon (Ag-DLC) film to improve the seal performance. The failure of the servo-actuator was analyzed. Then, a series of Ag-DLC films was deposited; the structure and combined tribological performances of the Ag-DLC films were investigated. The results show that the intensity of the Ag (111) crystal face in the films increases with an increase of Ag content. The hardness, intrinsic stress, frictional coefficient, and wear rate of the films tend to decrease with the amount of doping metal. The a:C-Ag10.5% film exhibits optimal combined properties. The Ag doping makes the film toughness improve; both soft Ag particles and a graphitized top layer act as solid lubricants. Our findings may offer a novel approach to make DLC film applicable for improving the seal performance of hydraulic servo-actuator. Based on the experimental data, a mechanism behind the film modification of Ag-DLC film is also revealed.

Robust stability analysis of real-time hybrid simulation considering system uncertainty and delay compensation

Real-time hybrid simulation (RTHS) which combines physical experiment with numerical simulation is an advanced method to investigate dynamic responses of structures subjected to earthquake excitation. The desired displacement computed from the numerical substructure is applied to the experimental substructure by a servo-hydraulic actuator in real time. However, the magnitude decay and phase delay resulted from the dynamics of the servo-hydraulic system affect the accuracy and stability of a RTHS. In this study, a robust stability analysis procedure for a general single-degree-of-freedom structure is proposed which considers the uncertainty of servo-hydraulic system dynamics. For discussion purposes, the experimental substructure is a portion of the entire structure in terms of a ratio of stiffness, mass, and damping, respectively. The dynamics of the servo-hydraulic system is represented by a multiplicative uncertainty model which is based on a nominal system and a weight function. The nominal system can be obtained by conducting system identification prior to the RTHS. A first-order weight function formulation is proposed which needs to cover the worst possible uncertainty envelope over the frequency range of interest. Then, the Nyquist plot of the perturbed system is adopted to determine the robust stability margin of the RTHS. In addition, three common delay compensation methods are applied to the RTHS loop to investigate the effect of delay compensation on the robust stability. Numerical simulation and experimental validation results indicate that the proposed procedure is able to obtain a robust stability margin in terms of mass, damping, and stiffness ratio which provides a simple and conservative approach to assess the stability of a RTHS before it is conducted.