Research

Open AccessArticle

A Low-Cost Miniature Electrohydrostatic Actuator System

by

Travis Wiens

and

Brendan Deibert

Actuators 2020, 9(4), 130; https://doi.org/10.3390/act9040130 - 04 Dec 2020

Cited by 7 | Viewed by 2348

Abstract

Hydraulic linear actuators dominate in high power applications but are much less common in low power (<100 W) systems. One reason for this is the cost: electric actuators in this power range generally exhibit lower performance but are also much less expensive than [...] Read more.

Hydraulic linear actuators dominate in high power applications but are much less common in low power (<100 W) systems. One reason for this is the cost: electric actuators in this power range generally exhibit lower performance but are also much less expensive than hydraulic systems. However, in recent years, some miniature hydraulic components have been mass produced, driving down prices. This paper presents the application of these low-cost components, together with a novel very low-cost 3D-printed valve to create an electrohydrostatic actuator. Capable of very high power and force density, this system is competitive on cost with lower-performing electric actuators. This paper presents models for the system’s performance, as well as experimental validation data. Full article

(This article belongs to the Special Issue Electro-Hydraulic Actuators)

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Open AccessArticle

Hydraulic Switching Control Supplementing Speed Variable Hydraulic Drives

by

,

,

and

Actuators 2020, 9(4), 129; https://doi.org/10.3390/act9040129 - 04 Dec 2020

Cited by 5 | Viewed by 2241

Abstract

Primary control of linear motion by variable speed electric motors driving a hydraulic cylinder via a constant displacement pump is an established and successful concept with a frequent use in industry. One problem arises when low or zero motion speed has to be [...] Read more.

Primary control of linear motion by variable speed electric motors driving a hydraulic cylinder via a constant displacement pump is an established and successful concept with a frequent use in industry. One problem arises when low or zero motion speed has to be realized under high pump pressure conditions. Such load scenarios occur frequently in certain pressing processes, e.g., for sintering or veneering. Most pumps have a lower speed limit, below which critical tribological conditions occur which impair lifespan and efficiency. In addition, pump speed control and pump fluctuation suffer from the mixed lubrication conditions in such an operation range. For a circumvention of such low speed pump operation, a digital valve control concept is presented and studied in this paper. Valve control is used in load holding phases with low speed. Pressure is provided by an accumulator which is charged by the pump in short charging cycles at reasonable pump speeds. It is shown that the mean control error during load holding phase lies within the desired band and the fluctuations of the control force are lower than those of the pump control. In addition, the unfavorable pump operation conditions can be avoided via digital control. Full article

(This article belongs to the Special Issue Electro-Hydraulic Actuators)

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Open AccessArticle

Control and Performance Analysis of Variable Speed Pump-Controlled Asymmetric Cylinder Systems under Four-Quadrant Operation

by

Shuzhong Zhang

,

Su Li

and

Tatiana Minav

Actuators 2020, 9(4), 123; https://doi.org/10.3390/act9040123 - 28 Nov 2020

Cited by 11 | Viewed by 2282

Abstract

Since the energy crisis, the further development of a variable speed pump-controlled hydraulic system driven by an electric machine has attracted increasing attention during the past few years. As a response to this, an innovative double pump-controlled asymmetric cylinder system (DPC) and its [...] Read more.

Since the energy crisis, the further development of a variable speed pump-controlled hydraulic system driven by an electric machine has attracted increasing attention during the past few years. As a response to this, an innovative double pump-controlled asymmetric cylinder system (DPC) and its control method are proposed in this study. The purpose of this study is to investigate the performance of two variable speed pump-controlled systems for asymmetric cylinders under a four-quadrant operating condition, in comparison with single pump control (SPC). The four-quadrant operating principles of the two systems are analyzed by simulation. Simulation models for both systems are introduced, and a position control method is proposed, with a tracking differentiator and speed feedforward, plus proportional-integral-derivative (PID) for four-quadrant operation. The DPC model was validated with the measurement of a crane. The simulations using the validated model were performed with a position reference and a varying load (four-quadrant operating arm of an excavator). The results demonstrated that the velocity fluctuation is eliminated by using the DPC instead of the SPC, and the position control performance of the DPC is better compared to the SPC, although the energy efficiency decreases slightly. Hence, the proposed DPC and its position control method are feasible for the four-quadrant operation of asymmetric cylinders. Full article

(This article belongs to the Special Issue Electro-Hydraulic Actuators)

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Open AccessArticle

Static and Dynamic Characterization and Control of a High-Performance Electro-Hydraulic Actuator

by

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and

Actuators 2020, 9(2), 46; https://doi.org/10.3390/act9020046 - 25 Jun 2020

Cited by 6 | Viewed by 8325

Abstract

This paper characterizes the static, dynamic, and controlled behavior of a high-performance electro-hydraulic actuator to assess its suitability for use in evaluating machine tool behavior. The actuator consists of a double-acting piston and cylinder arrangement controlled by a servo valve and a separate [...] Read more.

This paper characterizes the static, dynamic, and controlled behavior of a high-performance electro-hydraulic actuator to assess its suitability for use in evaluating machine tool behavior. The actuator consists of a double-acting piston and cylinder arrangement controlled by a servo valve and a separate rear chamber controlled by a separate valve, designed to work in conjunction to generate static forces of up to 7000 N that can be superposed with dynamic forces of up to ±1500 N. This superposition of periodic forces with a non-zero mean makes the actuator capable of applying realistic loading conditions like those experienced by machines during cutting processes. To characterize the performance of this actuator, linearized static and dynamic models are described. Since experiments with the actuator exhibit nonlinear characteristics, the linearized static model is expanded to include the influence of nonlinearities due to flow, leakages, saturations, and due to friction and hysteresis. Since all major nonlinearities are accounted for in the expanded static model, the dynamical model remains linear. Unknown static and dynamical model parameters are calibrated from experiments, and the updated models are observed to capture experimentally observed behavior very well. Validated models are used to tune the proportional and integral gains for the closed-loop control strategy, and the model-based tuning in turn guides appropriate closed-loop control of the actuator to increase its bandwidth to 200 Hz. The statically and dynamically characterized actuator can aid machine tool structural testing. Moreover, the validated models can instruct the design and development of other higher-performance electro-hydraulic actuators, guide the conversion of the actuator into a damper, and also test other advanced control strategies to further improve actuator performance. Full article

(This article belongs to the Special Issue Electro-Hydraulic Actuators)

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Open AccessArticle

Comparative Energy Analysis of a Load Sensing System and a Zonal Hydraulics for a 9-Tonne Excavator

by

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and

Actuators 2020, 9(2), 39; https://doi.org/10.3390/act9020039 - 20 May 2020

Cited by 22 | Viewed by 4455

Abstract

With the rising demand for energy efficiency, displacement-controlled or so-called pump-controlled systems have become an attractive research topic for applications in construction machinery and other off-road vehicles. Pump-controlled systems can be implemented with electro-hydrostatic actuators as electro-hydraulic zones, which are located next to [...] Read more.

With the rising demand for energy efficiency, displacement-controlled or so-called pump-controlled systems have become an attractive research topic for applications in construction machinery and other off-road vehicles. Pump-controlled systems can be implemented with electro-hydrostatic actuators as electro-hydraulic zones, which are located next to the end actuator as a replacement for the traditional valve-controlled hydraulic actuation systems. In this paper a 9-tonne class excavator is utilized as a study case. A mathematical model of the conventional machine, validated with tests carried out on both the excavator and the single hydraulic components, was previously developed within the Simcenter AMESim^© environment. This mathematical model was modified with electric components for simulating a zonal hydraulics excavator and compared with a conventional load sensing (LS) machine. The energy efficiencies of both the LS circuit and the new solution were evaluated for typical duty cycles, pointing out the obtainable energy efficiency improvements, which were mainly due to the absence of the directional valves and pressure compensators. The results also point out the effect of the pipe losses when the circuit layout requires the pipe for connecting the pump with the actuator; moreover, the effect of a diesel engine downsizing on the energy saving was evaluated. Full article

(This article belongs to the Special Issue Electro-Hydraulic Actuators)

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Open AccessArticle

A Novel Solution for the Elimination of Mode Switching in Pump-Controlled Single-Rod Cylinders

by

Petter H. Gøytil

,

Damiano Padovani

and

Michael R. Hansen

Actuators 2020, 9(1), 20; https://doi.org/10.3390/act9010020 - 14 Mar 2020

Cited by 18 | Viewed by 4263

Abstract

This paper concerns the stability issue of pump-controlled single-rod cylinders, known as mode switching. First, a review of the topic is provided. Thereafter, the most recently proposed solution for the elimination of mode switching is investigated and shown to result in unstable behavior [...] Read more.

This paper concerns the stability issue of pump-controlled single-rod cylinders, known as mode switching. First, a review of the topic is provided. Thereafter, the most recently proposed solution for the elimination of mode switching is investigated and shown to result in unstable behavior under certain operating conditions. A theoretical analysis is provided demonstrating the underlying mechanisms of this behavior. Based on the analysis, a novel control strategy is proposed and investigated numerically. Proper operation and stability are demonstrated for a wide range of operating conditions, including situations under which the most recently proposed solution results in unstable behavior and loss of control over the actuator. Full article

(This article belongs to the Special Issue Electro-Hydraulic Actuators)

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Open AccessArticle

Effect of Energy Recovery on Efficiency in Electro-Hydrostatic Closed System for Differential Actuator

by

,

,

and

Actuators 2020, 9(1), 12; https://doi.org/10.3390/act9010012 - 25 Feb 2020

Cited by 16 | Viewed by 5541

Abstract

This paper investigates energy efficiency and dynamic behavior through simulation and experiments of a compact electro-hydrostatic actuator system (EHA) consisting of an electric motor, external gear pump/motors, hydraulic accumulator, and differential cylinder. Tests were performed in a stand-alone crane in order to validate [...] Read more.

This paper investigates energy efficiency and dynamic behavior through simulation and experiments of a compact electro-hydrostatic actuator system (EHA) consisting of an electric motor, external gear pump/motors, hydraulic accumulator, and differential cylinder. Tests were performed in a stand-alone crane in order to validate the mathematical model. The influence and importance of a good balance between pump/motors displacement and cylinder areas ratios is discussed. The overall efficiency for the performed motion is also compared considering the capability or not of energy recovery. The results obtained demonstrate the significant gain of efficiency when working in the optimal condition and it is compared to the conventional hydraulic system using proportional valves. The proposed system presents the advantages and disadvantages when utilizing components off-the-shelf taking into account the applicability in mobile and industrial stationary machines. Full article

(This article belongs to the Special Issue Electro-Hydraulic Actuators)

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Open AccessArticle

A Comparison Study of a Novel Self-Contained Electro-Hydraulic Cylinder versus a Conventional Valve-Controlled Actuator—Part 1: Motion Control

by

Daniel Hagen

,

Damiano Padovani

and

Martin Choux

Actuators 2019, 8(4), 79; https://doi.org/10.3390/act8040079 - 05 Dec 2019

Cited by 20 | Viewed by 6552

Abstract

This research paper presents the first part of a comparative analysis of a novel self-contained electro-hydraulic cylinder with passive load-holding capability against a state of the art, valve-controlled actuation system that is typically used in load-carrying applications. The study is carried out on [...] Read more.

This research paper presents the first part of a comparative analysis of a novel self-contained electro-hydraulic cylinder with passive load-holding capability against a state of the art, valve-controlled actuation system that is typically used in load-carrying applications. The study is carried out on a single-boom crane with focus on the control design and motion performance analysis. First, a model-based design approach is carried out to derive the control parameters for both actuation systems using experimentally validated models. The linear analysis shows that the new drive system has higher gain margin, allowing a considerably more aggressive closed-loop position controller. Several benefits were experimentally confirmed, such as faster rise time, 75% shorter settling time, 61% less overshoot, 66% better position tracking, and reduction of pressure oscillations. The proposed control algorithm is also proven to be robust against load variation providing essentially the same position accuracy. In conclusion, the novel self-contained system is experimentally proven to be a valid alternative to conventional hydraulics for applications where passive load-holding is required. Full article

(This article belongs to the Special Issue Electro-Hydraulic Actuators)

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Open AccessArticle

A Comparison Study of a Novel Self-Contained Electro-Hydraulic Cylinder versus a Conventional Valve-Controlled Actuator—Part 2: Energy Efficiency

by

Daniel Hagen

,

Damiano Padovani

and

Martin Choux

Actuators 2019, 8(4), 78; https://doi.org/10.3390/act8040078 - 05 Dec 2019

Cited by 16 | Viewed by 5929

Abstract

This research paper presents the second part of a comparative analysis of a novel self-contained electro-hydraulic cylinder with passive load-holding capability against a state of the art, valve-controlled hydraulic system that is typically used in load-carrying applications. After addressing the control design and [...] Read more.

This research paper presents the second part of a comparative analysis of a novel self-contained electro-hydraulic cylinder with passive load-holding capability against a state of the art, valve-controlled hydraulic system that is typically used in load-carrying applications. After addressing the control design and motion performance in the first part of the study, the comparison is now focused on the systems’ energy efficiency. It is experimentally shown that the self-contained solution enables 62% energy savings in a representative working cycle due to its throttleless and power-on-demand nature. In the self-contained drive, up to 77% of the energy taken from the power supply can be used effectively if the recovered energy is reused, an option that is not possible in the state of the art hydraulic architecture. In fact, more than 20% of the consumed energy may be recovered in the self-contained system during the proposed working cycle. In summary, the novel self-contained option is experimentally proven to be a valid alternative to conventional hydraulics for applications where passive load-holding is required both in terms of dynamic response and energy consumption. Introducing such self-sufficient and completely sealed devices also reduces the risk of oil spill pollution, helping fluid power to become a cleaner technology. Full article

(This article belongs to the Special Issue Electro-Hydraulic Actuators)

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