Search

The pressure compensator is an important equipment of the deep-sea hydraulic system to provide the functions of pressure and volume compensation. In this paper, the structure features and static force analysis of the pressure compensator are studied. The physical model of the pressure compensator is established, and its dynamic characteristics influenced by the ambient pressure, the compensated flow and the temperature change are all analyzed. The entire working process of the pressure compensator is then researched. Therefore, two design criteria for reliability and dynamic characteristics respectively are proposed. A pressure compensator for 6000 m deep in the sea was designed and manufactured. Simulations and high-pressure experiments of the designed pressure compensator were conducted. The results show that the dynamic response of the compensated pressure under each input is all composed of a ramp change, a step change and a damped oscillation. The effective area of the rolling diaphragm, the spring stiffness and the mass of the diaphragm-piston assembly are the key design parameters to ensure the reliability and good dynamic characteristics of the pressure compensator. Simulation and high-pressure experiments verified the volume and pressure compensation function of the pressure compensator in the deep-sea environment. [ABSTRACT FROM AUTHOR]

Featured Application: In this study, the main components of the flexible support system (FSS) are optimized for multi-objective parameters using the finite element method, to reduce the internal resistance of the FSS and improve the consistency of force output. The hardness of rolling diaphragm (RD) is determined by the pressure test of the FSS. The actual resistance of the support cylinder at each movement position is determined by the internal resistance test, and the consistency of the value of each support cylinder is determined by the force output consistency test. It provides a theoretical basis for the application of the FSS in the optical mirror processing stage. During the processing of an optical mirror, the performance parameters of the bottom support system would affect the surface forming accuracy of the mirror. The traditional bottom support system has a large unadjustable support stiffness, which increases the difficulty of unloading the impact force generated by the grinding disc. In response to this scenario, a flexible support system (FSS) consisting of 36 support cylinders with beryllium bronze reeds (BBRs) and rolling diaphragms (RDs) as key components is designed. It is necessary to analyze the key components of the support cylinder to reduce its axial movement resistance, ensure a consistent force output of each support point. First, the internal resistance model of a flexible support cylinder is established, and the main factors of internal resistance are then analyzed. Thereafter, the multi-objective structural parameters of the BBR and RD are simulated in ANSYS using the control variable method. The optimal structural parameters of BBR and RD are determined by simulation. Finally, experiments are performed on the RD ultimate pressure, internal resistance of the support cylinder, and consistency of the force output of the FSS. The experimental results show that the support cylinder with the optimized design has good force output consistency, which provides a theoretical basis for the application of FSS in optical mirror processing. [ABSTRACT FROM AUTHOR]

Muscle models and animal observations suggest that physical damping is beneficial for stabilization. Still, only a few implementations of physical damping exist in compliant robotic legged locomotion. It remains unclear how physical damping can be exploited for locomotion tasks, while its advantages as sensor-free, adaptive force- and negative work-producing actuators are promising. In a simplified numerical leg model, we studied the energy dissipation from viscous and Coulomb damping during vertical drops with ground-level perturbations. A parallel spring- damper is engaged between touch-down and mid-stance, and its damper auto-decouples from mid-stance to takeoff. Our simulations indicate that an adjustable and viscous damper is desired. In hardware we explored effective viscous damping and adjustability, and quantified the dissipated energy. We tested two mechanical, leg-mounted damping mechanisms: a commercial hydraulic damper, and a custom-made pneumatic damper. The pneumatic damper exploits a rolling diaphragm with an adjustable orifice, minimizing Coulomb damping effects while permitting adjustable resistance. Experimental results show that the leg-mounted, hydraulic damper exhibits the most effective viscous damping. Adjusting the orifice setting did not result in substantial changes of dissipated energy per drop, unlike adjusting the damping parameters in the numerical model. Consequently, we also emphasize the importance of characterizing physical dampers during real legged impacts to evaluate their effectiveness for compliant legged locomotion.

During the processing of an optical mirror, the performance parameters of the bottom support system would affect the surface forming accuracy of the mirror. The traditional bottom support system has a large unadjustable support stiffness, which increases the difficulty of unloading the impact force generated by the grinding disc. In response to this scenario, a flexible support system (FSS) consisting of 36 support cylinders with beryllium bronze reeds (BBRs) and rolling diaphragms (RDs) as key components is designed. It is necessary to analyze the key components of the support cylinder to reduce its axial movement resistance, ensure a consistent force output of each support point. First, the internal resistance model of a flexible support cylinder is established, and the main factors of internal resistance are then analyzed. Thereafter, the multi-objective structural parameters of the BBR and RD are simulated in ANSYS using the control variable method. The optimal structural parameters of BBR and RD are determined by simulation. Finally, experiments are performed on the RD ultimate pressure, internal resistance of the support cylinder, and consistency of the force output of the FSS. The experimental results show that the support cylinder with the optimized design has good force output consistency, which provides a theoretical basis for the application of FSS in optical mirror processing.

In this paper an ECF-jet driven microhydraulic piston actuator is proposed and a large model is developed and its characteristics are evaluated. ECF is a kind of functional fluid which generates a jet flow by applying DC voltage. The developed actuator is mainly composed of two rolling diaphragms, a bidirectional ECF-jet generator and a piston. The inside of the actuator is filled with ECF and enclosed by the rolling diaphragms. The ECF-jet generator transfers ECF from one rolling diaphragm to the other, leading to contraction of one rolling diaphragm and expansion of the other, which drives the actuator. Since the developed actuator has a simple structure with a built-in pump and a tank without pipelines, and output forces do not depend on the displacement of the actuator, it is suitable for a microhydraulic servo system. [ABSTRACT FROM AUTHOR]

A pressure compensator for an underwater hydraulic system is studied in this paper. The compensator is used to maintain the tank pressure of the underwater hydraulic system so that it is slightly greater than the ambient pressure, allowing the system to work at any depth. The dynamic characteristics of the pressure compensator are studied using theoretical analysis, simulation and experiment. The tank pressure changes due to the step flow to the tank coming from the motion of a piston in a single-rod cylinder. This flow is caused by the unequal areas of the piston. The tank pressure change can be mathematically determined. A design procedure focusing on the dynamic characteristics of the pressure compensator is given. A compensator and underwater hydraulic system were built and the dynamic characteristics of the compensator were tested. Both simulation and experimental results conform to the analysis. The study provides a theoretical way to determine the dynamic characteristics of a pressure compensator in an underwater hydraulic system. [ABSTRACT FROM PUBLISHER]

An oil-based pressure-compensated underwater hydraulic system is designed and tested in this article. The underwater hydraulic system is equipped with a pressure compensator so that the tank pressure is always balanced with the ambient pressure. The system pressure is thus built on the ambient pressure. In this way, the underwater hydraulic system can work at any water depth. The steady-state characteristics of a spring-loaded pressure compensator are studied. The pressure compensator, underwater hydraulic power unit and the underwater valve control unit are designed and built. The whole underwater hydraulic system is tested in a high-pressure water simulator with lighting and video system in it. Results show that the underwater hydraulic cylinder can be driven properly under high water pressure, which demonstrates the effectiveness of the pressure compensation in the underwater hydraulic system. [ABSTRACT FROM PUBLISHER]

Abstract: Hydraulic accumulators are used in a variety of applications to minimize the pressure variation in hydraulic circuits and to store energy. Conventional hydraulic accumulators suffer from two major limitations, the hydraulic system pressure varies with the quantity of energy stored and the energy density is significantly lower than other energy domains. In this paper, a novel hydraulic accumulator is presented that uses a piston with an area that varies with stroke to maintain a constant hydraulic system pressure while the gas pressure changes. The variable area piston is sealed with a fabric reinforced rolling diaphragm. In this work, the piston radius profile is developed as a function of the piston displacement and then transformed into a function of the axial contact location between the piston and the diaphragm. The piston profile was solved numerically for a variety of conditions using both transformation methods to illustrate the geometric design trade-offs. Using a variable area gas piston with a fixed cylinder area, the maximum gas volume ratio was 1.8:1. An analysis of the energy density revealed that the constant pressure accumulator provides a 16% improvement in energy density over a conventional accumulator at a volume ratio of 2.71:1 and also exceeds the maximum energy density of a conventional accumulator at the lower volume ratio of 1.8:1. This new promising technology maintains a constant hydraulic system pressure independent of the quantity of energy stored, easing system control and allowing other circuit components to be downsized to meet the same power requirements, while also increases the energy storage density. [Copyright &y& Elsevier]