This exciting new reference text is concerned with fluid power control. It is an ideal reference for the practicing engineer and a textbook for advanced courses in fluid power control. In applications in which large forces and/or torques are required, often with a fast response time, oil-hydraulic control systems are essential. They excel in environmentally difficult applications because the drive part can be designed with no electrical components and they almost always have a more competitive power/weight ratio compared to electrically actuated systems. Fluid power systems have the capability to control several parameters, such as pressure, speed, position, and so on, to a high degree of accuracy at high power levels. In practice there are many exciting challenges facing the fluid power engineer, who now must preferably have a broad skill set.

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Fundamentals of Fluid Power Control

CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances

To reduce the surgical trauma to the patient, minimally invasive surgery is gaining considerable importance since the eighties. More recently, robot assisted minimally invasive surgery was introduced to enhance the surgeon's performance in these procedures. This resulted in an intensive research on the design, fabrication and control of surgical robots over the last decades. A new development in the field of surgical tool manipulators is presented in this article: a flexible manipulator with distributed degrees of freedom powered by microhydraulic actuators. The tool consists of successive flexible segments, each with two bending degrees of freedom. To actuate these compliant segments, dedicated fluidic actuators are incorporated, together with compact hydraulic valves which control the actuator motion. Especially the development of microvalves for this application was challenging, and are the main focus of this paper. The valves distribute the hydraulic power from one common high pressure supply to a series of artificial muscle actuators. Tests show that the angular stroke of the each segment of this medical instrument is 90°.

Integrated high pressure microhydraulic actuation and control for surgical instruments.

Numerical simulation and experimental research of the flow force and forced vibration in the nozzle-flapper valve

An assembly for a wheeled platform includes a platform element adapted to be attachable to a platform and a housing adapted to receive the platform element, wherein a change in a contact point of the platform element relative to the housing results in a turning response of the wheeled platform.

Truck assembly for a skateboard, wheeled platform, or vehicle

An electrohydraulic servovalve that uses fresh water as a pressure medium (water hydraulic servovalve) is developed. conventional electrohydraulic servovalve cannot be operated with such a hostile fluid. In this paper, we explain the structure and functions of components, and the relationship between them, as well as the developmental procedure of the water hydraulic servovalve. The basic idea for the servovalve is to support the spool of the valve with hydrostatic bearings and to lead the water from the bearings to the flapper-nozzle system. The hydrostatic bearings constitute a laminar restriction that takes the place of the turbulent restriction in the conventional flapper-nozzle system. We also explain the design procedure of the hydrostatic bearing in the valve and the relationship between electromagnetic elements and fluidic elements. The water hydraulic servovalves fabricated show good characteristics of smooth motion, endurance and controllability, as well as good dynamic characteristics.

Development of a Water Hydraulic Servovalve.

Development of a Water Hydraulic Servovalve

A vane type rotary machine such as a vane pump and a vane motor, wherein a rotor (15) having vanes (60) is stored in a cam casing (10) and a spindle (40) of a rotor (15) is pivoted rotatably on bearing parts (200, 250), working fluid on a delivery port (13) side is branched into flow paths (180) so as to lead it to the bearing parts (200, 250), and working fluid leading recessed parts (220) formed by a reduction in diameter of the spindle (40) are formed in the spindle (40) at positions where the bearing parts (200, 250) are provided so as to lead the working fluid into the working fluid recessed parts (220).

Vane type rotary machine

In this paper, flow force due to nozzle flow and its influence on the flapper-nozzle system for water hydraulic servovalves are discussed. The flow force acting on the flapper is estimated using the momentum theory, and expressed as a function of the nozzle pressure and flapper-nozzle gap. Analysis shows that the double nozzle flapper gives a quasi-linear characteristic to the relationship among the force on the flapper, the flapper gap and the spool velocity. The numerical result based on the theory is used to estimate the accuracy of the classical linear approximation. The moment due to the flow force resists input moment acting on the armature. Consequently the flow force reduces the magnitude of the change of the nozzle backpressures that drive the spool of the water hydraulic valve. Experimental verification of the theory is also presented.

Influence of Flow Force on the Flapper of a Water Hydraulic Servovalve.

A compact and lightweight water hydraulic motor has been developed with the aim of applying to water hydraulic systems that utilize tap water as the transfer medium of energy The developed water hydraulic motor, which drives in the low-pressure range equal or less than 20MPa, has power equivalent to 100W Structurally based on a balanced vane type motor, it has achieved high efficiency and durability through structural improvements, use of most suitable materials selected in order to minimize energy losses

Chishiro Yamashina

Papers

Development of a Water Hydraulic Servovalve.

Development of a Water Hydraulic Servovalve

Vane type rotary machine

Influence of Flow Force on the Flapper of a Water Hydraulic Servovalve.

Development of a low-pressure water hydraulic motor