The spring tube is the core component of the hydraulic servo valve, and its stiffness characteristics determine the sensitivity of the servo valve. For the difficulty in measuring and ensuring the stiffness of spring tube in complex structures, based on the principle of structural characteristics and stiffness measurement, an effective method for measuring and evaluating the stiffness of spring tube was proposed. Firstly, by the force analysis of the spring tube in the valve structure, using improved stiffness measurement theory, an equivalent measurement model of single-arm is established. Secondly, the stiffness measurement system of the spring tube is constructed based on this model. Furthermore, using the deformation and the spatial position recurrence method, the accuracy of the measurement system is further improved. Thirdly, using the orthogonal test method and linear optimization method of the Neural network model, the stiffness characteristics of the spring tube under the influence of different factors are studied further. Finally, the validity of the models is verified by using the software COMSOL and the experimental platform. The stability of the effective stiffness for the spring tube is further analyzed by the measurement data. The contribution and novelty of this paper are that based on the force analysis of the spring tube in the servo valve internal structure, an effective and systematic stiffness measurement and evaluation method are proposed. On this basis, experiments and stiffness characteristics analysis are carried out. Furthermore, several structural factors affecting the stiffness characteristics of spring tube are considered, and the stiffness characteristics of spring tube are systematically studied and analyzed. Based on this research and analysis, the systematic study of measurement and characteristics of precision components is very important for practical complex systems in this field. This makes it possible to further study the measurement of precision components which are difficult to measure in the actual structure. It is instructive to study the characteristics of precision components in complex structures.

The present research concentrates on the performance improvement of a two-stage proportional valve with internal hydraulic position feedback which is named as the Valvistor valve. In this paper, the performance constraint of this valve is identified and a novel electronic closed-loop control strategy with an integral-separation fuzzy proportional-integral-derivative controller is proposed to improve the valve performance, including the static characteristics and the dynamic characteristics. The results show that in the Valvistor valve, the comparison point and the feedback loop for the internal hydraulic position feedback is only in the main stage, while the input is in the pilot stage. This leads to the poor performance of this valve. The control strategy is very effective and the performance of the Valvistor valve is improved. With the control strategy, the error of the poppet displacement is reduced from 4.9% to 2.1% by adjusting the spool displacement in the pilot stage in real-time and the flow error is reduced from 5.3% to 2.3%. The dead zone of the poppet displacement and the flow is eliminated. The hysteresis is reduced from 5.3% to 2.6% and the linearity is improved. The overshoot is reduced from 0.06 to 0.02 mm and the settling time is reduced from 0.5 to 0.2 s. Moreover, the bandwidth is increased from 8 to 16 Hz.

Hydraulic pressure ripple in a pump, as a result of converting rotational power to fluid power, continues to be a problem faced when developing hydraulic systems due to the resulting noise generated. In this paper, we present simulation results from leveraging an actor-critic reinforcement learning method as the control method for active noise control in a hydraulic system. The results demonstrate greater than 96%, 81%, and 61% pressure ripple reduction for the first, second, and third harmonics, respectively, in a single operating point test, along with the advantage of feed forward like control for high bandwidth response during dynamic changes in the operating point. It also demonstrates the disadvantage of long convergence times while the controller is effectively learning the optimal control policy. Additionally, this work demonstrates the ancillary benefit of the elimination of the injection of white noise for the purpose of system identification in the current state of the art.

This paper reports a study on the static and dynamic behavior of pneumatic actuation systems, resulting in a comprehensive view of the influence of the system parameters on the energy efficiency and dynamic performance. The operating point approach based on the steady-state analysis of a pneumatic actuation system is used for developing analytical expressions to describe the relationship between the piston diameter and the system performance, including displacement time, stroke end velocity, and energy efficiency. The validity of the proposed equations is demonstrated by comparison with results from a test rig. Sensitivity analysis using a nonlinear dynamic simulation model indicated that a specific operating region exists, where good energy efficiency and the maximum dynamic performance are achieved. Moreover, the results show that an oversized system becomes more inefficient in both energetic and dynamic aspects. The results obtained provide a very consistent foundation for developing a method for pneumatic system sizing.

Resistor–capacitor (RC) response time models for pressurizing and depressurizing a pneumatic capacitor (mass accumulator) through a resistor (flow restriction) comprise a framework to systematically analyze complex fluidic circuits. A model for pneumatic resistance is derived from a combination of fundamental fluid mechanics and experimental results. Models describing compressible fluid capacitance are derived from thermodynamic first principles and validated experimentally. The models are combined to derive the ordinary differential equations that describe the RC dynamics. These equations are solved analytically for rigid capacitors and numerically for deformable capacitors to generate pressure response curves as a function of time. The dynamic pressurization and depressurization response times to reach 63.2% (or 1 − e − 1 ) of exponential decay are validated in simple pneumatic circuits with combinations of flow restrictions ranging from 100 μ m to 1 mm in diameter, source pressures ranging from 5 to 200 kPa, and capacitor volumes of 0.5 to 16 mL. Our RC models predict the response times, which range from a few milliseconds to multiple seconds depending on the combination, with a coefficient of determination of r 2 = 0.983 . The utility of the models is demonstrated in a multicomponent fluidic circuit to find the optimal diameter of tubing between a three-way electromechanical valve and a pneumatic capacitor to minimize the response time for the changing pressure in the capacitor. These lumped-parameter models represent foundational blocks upon which timing models of pneumatic circuits can be built for a variety of applications from soft robotics and industrial automation to high-speed microfluidics.

Reed valves are a type of check valve commonly found in a wide range of applications including air compressors, internal combustion engines, musical instruments, and even the human heart. While reed valves have been studied extensively in these applications, published research on the modeling and application of reed valves in hydraulic systems is sparse. Because the spring and mass components of a reed valve are contained in a single element, it is light and compact compared to traditional disk, poppet, or ball style check valves. These advantages make reed valves promising for use in high-frequency applications such as piston pumps, switch-mode hydraulics, and digital hydraulics. Furthermore, the small size and fast response of reed valves provide an opportunity to design pumps capable of operating at higher speeds and with lower dead volumes, thus increasing efficiency and power density. In this paper, a modeling technique for reed valves is presented and validated in a hydraulic piston pump test bed. Excellent agreement between modeled and experimentally measured reed valve opening is demonstrated. Across the range of experimental conditions, the model predicts the pump delivery with an error typically less than 1% with a maximum error of 2.2%.

Pneumatic artificial muscles (PAMs) are a compelling actuator for physical human–robot interaction (pHRI) due to their low mass, high-force capacity, and muscle-like characteristics. However, their low efficiency and bandwidth have forced mobile robotics researchers to examine alternative actuators for performing dynamic tasks like walking and grasping. Recently, the sleeve PAM, has been proposed and shown to improve the efficiency and force capacity when compared with traditional PAM designs. However, the increase in the dynamic performance of sleeve PAMs has not yet been studied. The aim of this research is to compare the dynamic performance of sleeve and traditional PAMS, and to develop a phenomenological model of their dynamic performance. Testing found that the isometric bandwidth of sleeve muscles can be 100% greater than that of traditional muscles at rest length if pressure response is considered, although this improvement decreases with contraction. If force is instead considered, the increase in bandwidth is even greater (up to 120% greater than that of a traditional PAM). The volume of both PAMs was determined using an experimental method, and a phenomenological model was fitted. When these models were used to simulate the performance of a PAM-actuated system, it was shown that both approximate the behavior of the measured system with good accuracy. Finally, a proposed implementation is given which illustrates how the benefits of the sleeved PAM actuator design could be realized in a practical robotics application.

In this paper, we propose a novel collocation method based on hybrid functions to identify the parameters and differential orders of fractional order systems (FOS). The hybrid functions consist of block-pulse functions and Taylor polynomials. The analytical form of Riemann–Liouville fractional order integral operator of these hybrid functions is derived using the Laplace transform. Then the integral operator is utilized, in conjunction with collocation points, to convert the FOS into an algebraic system directly. The parameters and differential orders of the FOS are estimated by minimizing the error between the output of the actual system and that of the estimated system. The effectiveness of the proposed method is verified through four examples.

The variation of the valve lift is a fairly common strategy currently adopted in several in-service internal combustion engines to optimize their performance depending on the operating conditions of the vehicle. The most critical aspect to consider during the conceptual design phase of a cam switch system is the extremely narrow window of opportunity to perform the cam change, which duration is defined by the time during which the corresponding valve lift is null. To meet this requirement and ensure safe, repeatable movements, a novel architecture based on the combination of a new electromechanical actuator and its dedicated control system is presented. The architecture is at first introduced with reference to the numerous examples available in the literature, and hence mathematically described. The dynamic model of the system derived from the presented equation is then used to study the performance of the presented solution and define its control strategy. Results are finally presented and discussed.

Productivity, reliability, controllability, flexibility, and affordable costs represent key aspects in mobile machines. Additionally, due to the high fuel price and the introduction of stringent emission regulations for diesel engines, the reduction of fuel consumption while persevering the existing performance is the current demand. In order to satisfy and maximize the above requirements, different hydraulic system architectures have been developed during the last decades. Both academia and industry have been investing considerable resources delivering numerous outcomes that require a classification. This review paper closes this gap by analyzing and classifying the working hydraulics of nonhybrid, valve-controlled mobile machines starting from the 1980s to the state of the art. Hydraulic layouts are addressed and categorized by both discussing their fundamentals and evolutions, and by pointing out their pros and cons in a way to provide the readers with a comprehensive overview of the systems currently available on the market and at the research stage.

A hydromechanical transmission (HMT) is a continuously variable transmission that transmits power both mechanically and hydraulically. A typical HMT consists of a pair of hydraulic pump/motors and a mechanical transmission in parallel, making it bulky and costly. The Hondamatic transmission is a compact alternative HMT design that uses an inline configuration such that the rotation of the piston barrels of the pump and motor is dual-used for mechanical transmission. This is achieved using a two-shafted pump that plays the role of a planetary gear (PG) and a distributor valve mechanism that replaces the valve plates. This paper provides the operating principle of this inline HMT (iHMT) and analyzes its performance through a combination of modeling and experimentation. Specifically, ideal and lossy average models are developed, and the performance of the Hondamatic is characterized experimentally. The lossy model, fitted with seven empirically determined parameters, is capable of predicting the mechanical and volumetric losses at different ratios and operating conditions. The dominant losses are found to be compressibility losses and no-load viscous friction losses, especially on the motor side. These losses are attributed to be the main causes for the unity transmission ratio to be less efficient than expected. The overall efficiency is between 74 and 86% at the conditions tested experimentally and is predicted to be over 70% under most operating conditions and transmission ratios. This analytical and experimental study is the first study in the open literature on this innovative compact inline HMT configuration.

Digital hydraulics is a new technology providing an alternative to conventional proportional or servovalve-controlled systems in the area of fluid power. Digital hydraulic applications, such as digital pumps, digital valves and actuators, switched inertance hydraulic converters (SIHCs), and digital hydraulic power management systems, promise high-energy efficiency and less contamination sensitivity. Research on digital hydraulics is driven by the need for highly energy efficient hydraulic machines but is relatively immature compared to other energy-saving technologies. This review introduces the development of SIHCs particularly focusing on the work being undertaken in the last 15 years and evaluates the device configurations, performance, and control strategies that are found in the current SIHC research. Various designs for high-speed switching valves are presented, and their advantages and limitations are compared and discussed. The current limitations of SIHCs are discussed and suggestions for the future development of SIHCs are made.

Based on the previously developed fixed-displacement asymmetric axial piston pump, a variable displacement asymmetric axial piston pump (VDAAPP) with three independent suction/delivery ports is proposed. A basic linear model of VDAAPP is established to get open-loop bode diagram. Based on open-loop Bode diagram features and design requirements, P-controller is determined for VDAAPP. Then VDAAPP's performance is investigated by advanced modeling environment for performing simulations of engineering systems (AMESim) and automatic dynamic analysis of mechanical systems (ADAMS) joint simulation, and some key design parameters are obtained. Next, a VDAAPP prototype with a maximum displacement of 40 cc/rev is designed and manufactured, ratio of flow rates at ports A, B and T is 1:0.6:0.4. Due to hard limitations of the test bench, the performance only under the conditions of the opposite passive loads is tested. Preliminary test results indicate that VDAAPP prototype works normally and meets the design requirements for flow ratio, and the maximum rise time of the test pressure is about 0.32 s. However, due to special design of VDAAPP valve plate, the swash plate torque severely limits system dynamic response. Therefore, an improved swashplate control system based on asymmetric-valve-controlled asymmetric-piston scheme is presented as well, it is found to be an effective way to suppress the negative impact of swash plate torque on system dynamic performance. This provides a direction for the optimization of the swashplate control system for asymmetric axial piston pumps in the future.

This article presents simulation data and measurements of a novel valve concept that features a soft landing concept. The purpose is to validate the design framework that has been applied to design the valve. The experimental results are obtained with a test rig manufactured specifically for this type of valve design. The validation includes studying the valves switching dynamics, cushion pressure dynamics, and movement-induced flow (MIF). The tests show that the tendencies are captured accurately although the exact magnitudes of forces do not match fully and a noticeable difference between simulated and measured plunger position is revealed. This amounts in a significant difference in the cushion pressure. Therefore, the pressure model is validated by using the measured lift and velocity derived hereof and this shows sufficient correspondence between the two pressures.

A force-controlled pneumatic actuator with long connecting tubes is a well-accepted solution to develop magnetic resonance imaging (MRI)-compatible force control applications. Such an actuator represents an uncertain, second-order, nonlinear system with input delay. The integral sliding mode control, because of guaranteed robustness against matched uncertainties throughout the system response, provides a favorable option to design a robust controller for the actuator. However, if the controller is based on a linear integral sliding surface (LISS), the response of the actuator overshoots, especially when there are large initial errors. Minimizing overshoot results in a smaller controller bandwidth and a slower system response. This paper presents a novel nonlinear integral sliding surface (NLISS) for a sliding mode controller to improve the transient response of the actuator. The proposed surface is a LISS augmented by a nonlinear function of tracking error and does not have a reaching phase when there are initial errors and even multiple steps in the desired trajectory. The surface enables the integral sliding mode controller to offer variable damping, which changes from low to high as the transient error approaches small values and vice versa. Simulation studies and experimental results show that the controller based on the proposed sliding surface successfully eliminates the overshoot without compromising the controller bandwidth, rise, and settling times. For performance evaluation, the controller parameters are tuned using the globalized and bounded Nelder–Mead (GBNM) algorithm with deterministic restarts. The study also establishes the asymptotic stability of the controller based on the proposed sliding surface using Lyapunov's stability criterion.

In digital displacement pump (DDP), the states of valves are nonlinear correlation with the instantaneous flow rate and flow fluctuation. For low-speed working condition, the digital valve has potential to switch several times to improve flow fluctuation. So, the relationship between the valve states and the flow rate is decoded, and a novel optimal fluctuation regulation (OFR) method including OFR-strict (OFR-S) and OFR-relaxation (OFR-R) is designed in this paper. The periodicity and the symmetry of OFR methods are proved and an optimal solution in the predefined minimum characteristic interval (MCI) is realized. Compared to the traditional sequential, partial, and pulse width modulation (PWM) methods, OFR-S has the minimum flow fluctuation, while OFR-R is preferred in low-speed ratio to reduce the digital valve switching frequency. At last, the effects of valve delay and oil compressibility are analyzed. As a theoretical precise optimal solution, OFR method demonstrates its ability in handling nonlinear problems in MCI. And it definitely will be a good base for the nonlinear controller design in the future.

This paper presents a novel hydrostatic actuator, which is named as linear-driven electro-hydrostatic actuator (LEHA). In an LEHA, the actuator is driven by a novel collaborative rectification pump (CRP), which incorporates two miniature cylinders and two spool valves. Specifically, the CRP is driven by two linear oscillating motors, which are designed and optimized to generate reciprocating motion at high frequency with adequate stroke. CRP offers a highly novel linear fluid pump with flexibility in bi-directionally driving. In this paper, schematic of LEHA is first presented and its kinematic flow rate equation is derived. Then the design of CRP, linear oscillating motor, as well as the whole LEHA prototype is introduced. Performance of the LEHA is demonstrated through a series of experiments and simulation, and analysis of the results is also included.

Using a unique inlet metering pump with fixed displacement and speed, this work introduces a new way to control a linear hydraulic actuator velocity. The inlet metering system consists of an inlet metering valve that adjusts the hydraulic fluid flow that enters the pump and a fixed displacement pump. Fluid is supplied to the inlet metering valve at a fixed pressure. Energy losses associated with flow metering in the system are reduced because the pressure drop across the inlet metering valve can be small compared to a traditional valve-controlled system. A velocity control system is designed using the inlet metering pump to control the fluid flow into a hydraulic cylinder. First, the valve dynamic model is ignored, the open-loop response is studied, and closed-loop proportional and proportional derivative controllers are designed. Next, the valve dynamic model is included and closed-loop proportional integral derivative, H ∞ , and two-degrees-of-freedom controllers are designed. Designs with the goals of stability and performance of the system are considered so that a precise velocity control system for the hydraulic cylinder is achieved. In addition to the potentially high efficiency of this system, there is potential for low-cost, fast-response, and less complicated dynamics compared to other systems. The results show that the velocity control system can be designed so that the system is stable for all cases and with 0% overshoot and no oscillation depending on valve dynamics using the two-degrees-of-freedom controller for tracking the desired velocity.

This paper studies the impact of using different types of energy storages integrated with a heat pump for energy efficiency in radiant-floor buildings. In particular, the performance of the building energy resources management system is improved through the application of distributed model predictive control (DMPC) to better anticipate the effects of disturbances and real-time pricing together with following the modular structure of the system under control. To this end, the load side and heating system are decoupled through a three-element mixing valve, which enforces a fixed water flow rate in the building pipelines. Hence, the building temperature control is executed by a linear model predictive control, which in turn is able to exchange the building information with the heating system controller. On the contrary, there is a variable action of the mixing valve, which enforces a variable circulated water flow rate within the tank. In this case, the optimization problem is more complex than in literature due to the variable circulation water flow rate within the tank layers, which gives rise to a nonlinear model. Therefore, an adaptive linear model predictive control is designed for the heating system to deal with the system nonlinearity trough a successive linearization method around the current operating point. A battery is also installed as a further storage, in addition to the thermal energy storage, in order to have the option between the charging and discharging of both storages based on the electricity price tariff and the building and thermal energy storage inertia. A qualitative comparative analysis has been also carried out with a rule-based heuristic logic and a centralized model predictive control (CMPC) algorithm. Finally, the proposed control algorithm has been experimentally validated in a well-equipped smart grid research laboratory belonging to the ERIGrid Research Infrastructure, funded by European Union's Horizon 2020 Research and Innovation Programme.

This paper has been written to develop closed-form equations for describing the theoretical displacement of a check-valve type, digital displacement pump. In theory, the digital displacement pump is used to alter the apparent volumetric displacement of the machine by short circuiting the flow path for reciprocating pistons within the machine that would ordinarily deliver a full volumetric flow rate to the discharge side of the pump. The short circuiting for the pistons is achieved by opening and closing a digital valve connected to each piston chamber at a desired time during the kinematic cycle for each reciprocating piston. Experience with these machines has shown that the expected volumetric displacement for the machine tends to decrease with pressure. This paper presents a theoretical explanation for the reduced volumetric displacement of the pump and quantifies the expected behavior based upon the digital valve command, the residual volume of fluid within a single piston chamber, and the fluid bulk modulus-of-elasticity. In summary, it shown that the apparent volumetric displacement of the machine may be reduced by as much as 10% for high-displacement commands and by as much as 30% for low-displacement commands.