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.
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.
Pneumatic actuators are low-cost, safe, clean and exhibit a high power to weight ratio. In this paper a novel control strategy for solving the tracking problem of pneumatic servo positioning systems ...copes with the nonlinearities of air flow through the 5/3-way proportional directional control valves and the nonlinear friction by considering position, velocity and pressure difference in the chambers of the pneumatic cylinder, as feedback states. The experimental and simulated results from the proposed tracking control strategy, probe that the time delay in the system that depends on the valve's flow rate and the size of the pneumatic cylinder, is low but cannot be eliminated and it is the main source of the obtained tracking error.
•Research results of a 4/3 sectional proportional directional control valve.•A concept of using flow forces for pressure compensation.•Proposition of creating the appropriate spool grooves to obtain ...required jet angle.•Obtaining dependency of spool position on jet angle and thus on flow forces.•Obtaining the required valve characteristics through the spring stiffness selection.
The main subject of this article is pressure compensation in a multi-section proportional directional control valve. The undertaken compensation task was carried out without the use of neither additional compensating valves nor other correcting elements, such as sensors in a feedback control system. The proposed method consists in the appropriate adjustment of forces acting on the valve spool. It requires knowledge of the electromagnet force characteristics and the appropriately matched stiffness and initial tension of the valve spring. In order to achieve the assumed objective, a number of CFD simulations was performed on a 3-D fluid model. The CFD analysis allowed determination of the values of flow resistance through the valve and the axial component of the flow force acting on the spool. The values calculated for various spool positions and flow velocities were approximated using analytical equations. Next, the mathematical model was built and simulations in Matlab/Simulink system were carried out. In the first stage of the research, flow characteristics of a single valve section were determined. The obtained results were then verified on the test bench. In the second stage, the simulation model was used to examine the possibility of pressure compensation in a three-section control valve. In this case, the individual valve sections were loaded unevenly by applying pressure in a wide range of values. It has been demonstrated, that the appropriate shaping of the spool geometry allows usage of the flow forces for pressure compensation in multi-section proportional directional control valves.
This article concerns flow analysis through a multi-section proportional control valve. In valves of this type, the flow rate is adjusted through an electromagnet current. However, for a fixed ...control signal value, the flow rate changes as the pressure in the system increases, which is an unfavorable phenomenon. Compensation for pressure influence is usually achieved using additional valves. In this work, the valve characteristics were modified to achieve a possibly steady flow rate by compensating for the pressure using flow forces without the necessity of correction valves. For this purpose, the geometry of the spool throttling slots was designed by making precise cuts. Moreover, the parameters of the return springs were adjusted accordingly. The changes were introduced in such a way as to adjust the direction of the fluid stream and thus influence the balance of forces acting on the spool. Simulation tests were performed using the CFD method. In turn, laboratory experiments were carried out using the PONAR WREM10 valve with a prototype spool in two neutral position flow configurations: closed (E) and open (W). The results confirmed the valve’s ability to maintain a quasi-constant flow rate in a wide pressure range. The maximum obtained non-uniformity in the flow rate for the fixed control signal in the whole studied pressure range, p = 5–30 MPa, was 6.3% except for the lowest current intensity, I=0.6 A, when it raised to 13.6%. Moreover, high consistency between simulation results and laboratory experiments was achieved. The difference in the obtained flow rate did not exceed 8–10% in the case of low current intensity values I=0.6–0.75 A, and it fell below 5% at higher ones.
The article compares the dynamic performances of the pump-controlled, valve-controlled and prime-mover controlled hydromotor drive systems for a wide range of operating conditions. The control ...strategy adopted for each of them varies the supply flow to the hydromotor that gives the regulated drive speed. In this respect, the Simscape models are developed for the said systems that are validated experimentally. On the basis of response time, overshoot, and steady-state error obtained from the simulation and test results, it is found that the valve controlled hydromotor drive system is more sensitive than the others; whereas, the load-sensing pump control requires more time to settle but has less overshoot.
•Three different control experiments are carried out to achieve a constant speed of a hydromotor under varying load.•The system parameters are estimated and validated by using optimization techniques.•It is established that the valve controlled hydromotor drive is more sensitive than others.•The load-sensing hydromotor drive is found to have a more sluggish response compared to the others.
This article proposes an effective methodology for the fluid-dynamic design optimization of the sliding spool of a hydraulic proportional directional valve: the goal is the minimization of the flow ...force at a prescribed flow rate, so as to reduce the required opening force while keeping the operation features unchanged. A full three-dimensional model of the flow field within the valve is employed to accurately predict the flow force acting on the spool. A theoretical analysis, based on both the axial momentum equation and flow simulations, is conducted to define the design parameters, which need to be properly selected in order to reduce the flow force without significantly affecting the flow rate. A genetic algorithm, coupled with a computational fluid dynamics flow solver, is employed to minimize the flow force acting on the valve spool at the maximum opening. A comparison with a typical single-objective optimization algorithm is performed to evaluate performance and effectiveness of the employed genetic algorithm. The optimized spool develops a maximum flow force which is smaller than that produced by the commercially available valve, mainly due to some major modifications occurring in the discharge section. Reducing the flow force and thus the electromagnetic force exerted by the solenoid actuators allows the operational range of direct (single-stage) driven valves to be enlarged.
In a hydraulic control system (herein, termed a major control loop), a proportional directional control (PDC) valve with spool position feedback may work in a minor (or inner) control loop. In this ...study the authors propose control designs to improve the performance of the PDC valve control loop (a minor control loop). At first, the mathematical model for the PDC valve is developed through an experimental identification process. Then, a dead-zone compensator that facilitates jumping of the overlap zone in spool/sleeve combination is devised and applied. A reference input following controller (including PI-D and feed-forward controller) that enables robust control of the PDC valve under disturbances is devised using the pole placement method and the zero placement method. Subsequently, an input shaping filter is incorporated into the devised control system to improve the reference following characteristic in high frequency range. Finally, the effectiveness of the proposed control design is verified experimentally.
An adaptive dynamic surface controller (ADSC), which comprises an online parameter estimator and a robust control law, is developed for the pneumatic servo systems driven by the proportional ...directional control valves. Departing from the use of time-consuming offline fitting of the orifice area to accommodate the effect of valve dead zone, this paper employs the least-square-type indirect parameter estimation algorithm with online condition monitoring to estimate the dead-zone parameters and some other important model parameters. These accurate estimates of model parameters are utilized in the development of a precise position tracking controller for the single-rod pneumatic actuator. By using the dynamic surface control technique to synthesize the robust control law, the problem of "explosion of complexity" in traditional backstepping design method is avoided. The stability of the closed-loop system is proved by the means of the Lyapunov theory. The obtained extensive comparative experimental results verify the effectiveness of the proposed valve dead-zone compensation strategy and the high-performance nature of the ADSC in practical implementation.
This paper proposes a novel actuation system for an offshore drilling application. It consists of three self-contained electro-hydraulic cylinders that can share and store regenerated energy. The ...energy saving potential of the proposed solution is analyzed through a multibody system simulation. The self-contained system demonstrates superior energy efficiency compared to the benchmark system representing the state-of-the-art approach used today (i.e., valve-controlled cylinders by means of pressure-compensated directional control valves and counter-balance valves, supplied by a centralized hydraulic power unit). Due to the power on demand capability, the cancellation of the throttling losses, and the opportunity to recover energy in motoring quadrants, the self-contained system consumes 83.44% less energy without affecting the system's performance.
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