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Traditional valve-controlled hydraulic cylinders are usually very inefficient due to power loss through the control valve. An efficient alternative architecture is to distribute power electrically rather than hydraulically to a group of cylinders and drive each cylinder via individual servomotor-driven pumps. This arrangement is called electrohydrostatic actuation. Such actuators are currently available for power ratings of several hundred watts or greater, but not in the sub-100W range. This paper details the design, simulation and testing of a piezopump which is intended to address this gap. The motivation is for aerospace applications, and in particular accessory actuators used in the landing gear system. The 10\,W-100\,W range is a high-power output for a piezopump, and to achieve this a novel design using disc-style reed valves was developed to allow pumping frequencies above 1kHz. These high frequencies necessitated the development of custom power electronics capable of delivering 950\,V peak-peak sine wave excitation to a largely capacitive load. Experimental results show that the piezopump is capable of delivering over 30\,W of hydraulic power, and at no-load can deliver up to 2\,L/min of flow at 1250\,Hz. Future development includes a transition to multi-cylinder pumps, and improved reed-valve modelling to improve the accuracy of simulated performance.

With large numbers of COVID-19 patients requiring mechanical ventilation and demand outstripping supply in some parts of the world, rapid development of new safe and effective ventilation systems has been an important activity since early 2020. Fluid power expertise is required for the design and implementation of the pneumatic system which is usually used for ventilator actuation. In addition, the external breathing circuit in which the patient is a part can also be understood, modelled and optimized using techniques familiar to fluid power engineers. Some examples of modelling approaches for both the internal and external ventilator circuitry are presented in this talk. In particular, a case study will be discussed in which a configuration with optimized restrictor valves is proposed to allow two patients to be connected to a single ventilator. Both simulation and experimental results indicate that pressure and flow (tidal volume) parameters can be adjusted individually for the two patients in this scenario by tailoring the restrictor valve settings.

Two - stage servovalves, despite being widely used in aircraft and industry because of their reliability and high performance, have a few disadvantages that are still unsolved at the state of the art, such as the power consumption caused by the quiescent flow (internal leakage) in the pilot stage, and the complexity and high number of parts of the torque motor assembly of the pilot stage. The solution to these problems can help to reduce costs, weight, power consumption, and to enhance the reliability and producibility as well as the performance of these valves. This paper presents a novel configuration of servovalve, which has the potential to overcome the above-mentioned issues. The proposed servo-valve includes a novel architecture for the pilot stage by using two piezo-electric actuators (ring benders). In this paper, the performance of this novel pilot stage is assessed. To this end, a valve prototype has been constructed and tested; the experimental results are also used to validate a numerical model obtained with the software Simscape Fluids. The results show that, acting on specific parameters, the performance of the piezo-valve can be very competitive, while ensuring very low internal leakage and complexity.

Animals exploit soft structures to move smoothly and effectively in complex natural environments. These capabilities have inspired robotic engineers to incorporate soft actuating technologies into their designs. Developing soft muscle-like actuation technology is one of the grand challenges in the creation of soft-body robots that can move, deform their body, and modulate body stiffness. This paper presents the development of smart pneumatic McKibben muscles woven and reinforced by using conductive insulated wires to equip the muscles with an inherent sensing capability, in which the deformation of the muscles can be effectively measured by calculating the change of wire inductance. Sensing performance of a variety of weaving angles is investigated. The ideal McKibben muscle models are used for analysing muscle performance and sensing accuracy. The experimental results show that the contraction of the muscles is proportional to the measured change of inductance. This relationship is applied to a PID control system to control the contraction of smart muscles in simulation, and good control performance is achieved. The creation of smart muscles with an inherent sensing capability and a good controllability is promising for operation of future soft robots.

Legged robots are dynamic moving machines that are potentially able to traverse through rough terrain which is inaccessible for wheeled or tracked vehicles. For bipedal robots, balancing control while hopping/running is challenging, especially when the foot contact area is small. Servo hydraulics is highly suitable for robot leg actuation due to its high power density and good power-to weight ratio. This paper presents a controller for a hydraulically actuated bipedal robot, the Bath Bipedal Hopper (BBH). The controller follows the well-established structure of the ‘Three-part’ control algorithm. The three parts are: hopping height control; longitudinal velocity control by changing the leg angle during the flight phase to place the foot in the desired position; and body attitude correction during the stance phase. Simulation results from a detailed non-linear model indicate that this controller can successfully balance the hydraulic robot while hopping with different longitudinal velocities.

It is believed that structures and actuation systems should be tightly integrated together in the future to create lightweight dynamic machines. This requires actuators to be distributed through the structure. A tensegrity structure is a very promising candidate for this future integration due to its potentially excellent stiffness and strength-to-weight ratio, and the inherent advantage of being a multi-element structure into which actuators can be embedded. In this paper, an antagonistic multi-axis control of a tensegrity structure is achieved, using a dead band controller. The controller is studied by the describing function technique, and a condition to guarantee stability is derived. The stability condition is illustrated with simulation and experimental results, and is used as a general rule to achieve stable control of the structure.

Additive manufacture gives the opportunity to create complex hydraulic components (e.g. valve bodies) which are of much reduced weight, only adding material where necessary. The geometry can be optimized to meet stringent design requirements, without the normal subtractive manufacturing constraints. For small production runs, for example production numbers typical in aerospace, manufacture can be very cost-effective, with high repeatability and low material waste. A significant reduction in part count and consequent simplification of assembly is also possible. With the dramatically increased speed of prototyping, AM promises a much shorter development cycle.In this talk, the potential and challenges of AM for hydraulic components are reviewed, focussing on the powder bed fusion laser melting process. A detailed example is given of an aerospace servovalve body additively manufactured from titanium alloy (Ti6Al4V) on a Renishaw AM250. Laser melting is known to be successful with this material, although research is still required to ensure the characteristics and quality are suitable for aerospace applications. In particular, fatigue life is affected by surface finish and microstructure, and the effects of build process parameters and heat treatment are just starting to be understood. Certification questions arise with flight actuators and using additive manufacturing for safety critical parts requires new standards to be developed. Examples of other hydraulic AM components are also reviewed, including manifolds, actuators and other types of valves, for both aerospace and industrial applications.

Background Tenofovir disoproxil fumarate can cause renal and bone toxic effects related to high plasma tenofovir concentrations. Tenofovir alafenamide is a novel tenofovir prodrug with a 90% reduction in plasma tenofovir concentrations. Tenofovir alafenamide-containing regimens can have improved renal and bone safety compared with tenofovir disoproxil fumarate-containing regimens. Methods In these two controlled, double-blind phase 3 studies, we recruited treatment-naive HIV-infected patients with an estimated creatinine clearance of 50 mL per min or higher from 178 outpatient centres in 16 countries. Patients were randomly assigned (1:1) to receive once-daily oral tablets containing 150 mg elvitegravir, 150 mg cobicistat, 200 mg emtricitabine, and 10 mg tenofovir alafenamide (E/C/F/tenofovir alafenamide) or 300 mg tenofovir disoproxil fumarate (E/C/F/tenofovir disoproxil fumarate) with matching placebo. Randomisation was done by a computer-generated allocation sequence (block size 4) and was stratified by HIV-1 RNA, CD4 count, and region (USA or ex-USA). Investigators, patients, study staff, and those assessing outcomes were masked to treatment group. All participants who received one dose of study drug were included in the primary intention-to-treat efficacy and safety analyses. The main outcomes were the proportion of patients with plasma HIV-1 RNA less than 50 copies per mL at week 48 as defined by the the US Food and Drug Adminstration (FDA) snapshot algorithm (pre-specified non-inferiority margin of 12%) and pre-specified renal and bone endpoints at 48 weeks. These studies are registered with ClinicalTrials.gov, numbers NCT01780506 and NCT01797445. Findings We recruited patients from Jan 22, 2013, to Nov 4, 2013 (2175 screened and 1744 randomly assigned), and gave treatment to 1733 patients (866 given E/C/F/tenofovir alafenamide and 867 given E/C/F/tenofovir disoproxil fumarate). E/C/F/tenofovir alafenamide was non-inferior to E/C/F/tenofovir disoproxil fumarate, with 800 (92%) of 866 patients in the tenofovir alafenamide group and 784 (90%) of 867 patients in the tenofovir disoproxil fumarate group having plasma HIV-1 RNA less than 50 copies per mL (adjusted difference 2·0%, 95% CI -0·7 to 4·7). Patients given E/C/F/tenofovir alafenamide had significantly smaller mean serum creatinine increases than those given E/C/F/tenofovir disoproxil fumarate (0·08 vs 0·12 mg/dL; p

In 2016 it is 70 years since the first patent for a two-stage servovalve was filed, and 60 years since the double nozzle-flapper two-stage valve patent was granted. This paper reviews the many alternative servovalve designs that were investigated at that time, focusing on two-stage valves. The development of single-stage valves – otherwise known as direct drive or proportional valves – for industrial rather than aerospace application is also briefly reviewed. Ongoing research into alternative valve technology is then discussed, particularly focussing on piezoelectric actuation and the opportunities afforded by additive manufacturing.

We describe a new two-stage aerospace servovalve which has an additively manufactured titanium body, and a small piezoelectrically actuated spool as its first stage, with electrical main stage position feedback. The approach promises to provide low weight, low leakage, and more accurate spool positioning. In addition, it enables increased manufacturing automation thereby reducing cost, increasing repeatability, and generates less waste material. Valve design, operation and measured performance are discussed in this paper.

The effectiveness of ZVD signal shaping in a closedloop for a hydraulic system is demonstrated. This is done byimplementing a control loop first in a simple simulation of asingle hydraulic actuator with a simple mass as loading. Thecontrol loop is then validated experimentally on a 2-linkarticulated hydraulic robot leg. Placing a ZVD filter inside aclosed-loop proportional controller improves performancewithout the use of high-speed controllers or accelerationfeedback which may be otherwise needed in order to achievegood position control performance of hydraulic actuators.

Planar control is an important first step in the development of more complex running robots. This extended abstract describes a technique for control of a one-legged planar robot hopping over discontinuous surfaces. In simulations the robot is tasked with traversing across terrain which provides limited surface for foot placement. The robot has to hop between foot placement surfaces placed at varying distances and heights. The controller has to adjust leg landing angle and leg extension in order to produce the parabolic flight trajectory necessary to land at the next targeted foot placement spot.

Non-linear model-based controller design enables high bandwidth motion control of servohydraulically actuated systems. In this paper, results are presented for three example systems from the structural testing industry: a pedestrian impact test system, a crash testing catapult, and an earthquake simulation table. An important element of such control systems is the provision of high accuracy, low noise feedback signals (for example combining position and acceleration measurements to improve motion estimation). Closed loop bandwidth well above the hydraulic resonant frequency is achievable.

Three-wheeled tilting vehicles have many potential advantages. They combine the comfort and safety of a car with the fuel economy, size and manoeuvrability of a motorcycle. One major challenge is to fully understand and account for the unusual dynamics of this type of vehicle. This paper sets out the equations of motion for a vehicle with single front and twin rear wheels and compares them with those of a car and a motorcycle. The mathematical model shows that it is necessary to introduce a tilt-dependent rear wheel steer term to obtain balanced handling characteristics. A vehicle with a hydraulically actuated tilting system is considered as a case study. As the tilt actuators act against the non-tilting engine module, this has significant effects on the cornering dynamics. Finally, the difference between the lateral acceleration and the hydraulic response time is shown to be a key issue.

Let G = (V,E) be a graph. A set R is a restrained dominating set (total restrained dominating set, resp.) if every vertex in V ? R (V) is adjacent to a vertex in R and (every vertex in V ?R) to a vertex in V ?R. The restrained domination number of G (total restrained domination number of G), denoted by gamma_r(G) (gamma_tr(G)), is the smallest cardinality of a restrained dominating set (total restrained dominating set) of G. If T is a tree of order n, then gamma_r(T) is greater than or equal to (n+2)/3. We show that gamma_tr(T) is greater than or equal to (n+2)/2. Moreover, we show that if n is congruent to 0 mod 4, then gamma_tr(T) is greater than or equal to (n+2)/2 + 1. We then constructively characterize the extremal trees achieving these lower bounds. Finally, if G is a graph of order n greater than or equal to 2, such that both G and G' are not isomorphic to P_3, then gamma_r(G) + gamma_r(G') is greater than or equal to 4 and less than or equal to n +2. We provide a similar result for total restrained domination and characterize the extremal graphs G of order n achieving these bounds.

Real-time substructure testing is an approach for assessing components of complex systems under realistic boundary conditions. This work shows the use of adaptive feedforward for the accurate and stable control of such tests. Methods based on least-mean-squares filters and based on recursive-least-squares filters are addressed. Moreover, the dissertation discusses methods for the practical implementation of the tests regarding measurement, simulation, and control. Echtzeit-Substrukturtests sind ein Ansatz zur Beurteilung von Komponenten komplexer Systeme unter realistischen Randbedingungen. Diese Arbeit zeigt den Einsatz von adaptiven Filtern für die genaue und stabile Regelung solcher Tests. Es werden Methoden gezeigt, die auf Least-Mean-Squares Filtern und Recursive-Least-Squares Filtern basieren. Darüber hinaus werden in der Dissertation Methoden zur praktischen Durchführung der Tests hinsichtlich Messung, Simulation und Regelung diskutiert.

Rapid development of Marine Renewable Energy Devices (MREDs) strongly focuses on tidal and wave sites, although little is known of impacts on surrounding ecosystems. Quantification of the behavior and distribution of animals around MREDs is crucial to understanding these impacts. The NERC/Defra collaboration FLOw, Water column and Benthic ECology (FLOWBEC) produced an innovative subsea platform [1], which includes an Imagenex multibeam echosounder oriented along the axis of tidal flow, and an EK60 multifrequency echosounder, identifying targets and characterising the morphology of turbulence. Co-registration and tracking [2] will be illustrated with examples from five 2-week deployments at the European Marine Energy Centre (EMEC) in Orkney.

Nanoporous silicon (pSi) films on a silicon wafer were loaded with sodium perchlorate and perfluoropolyether (PFPE) oxidizing agents. Sensitiveness to impact, friction and electrostatic discharge (ESD) of the resulting energetic thin films were investigated. It was observed that pSi loaded with perchlorate was sensitive at the lowest limit of detection for the available equipment (360 N). pSi loaded with either perchlorate or PFPE displayed behavior during sensitiveness testing similar to other primary explosive materials. Refereed/Peer-reviewed

A systematic study of nanoenergetic films consisting of nanostructured porous silicon impregnated with sodium perchlorate is carried out. The explosive properties of these films are investigated as a function of thickness, porosity, and confinement. The films' burning rates are investigated using fiber-optic velocity probes, demonstrating that flame-front velocities vary between approximately 1 and 500 m s(-1) and are very sensitive to the films' structural characteristics. Analysis of the flame profile by high-speed video is also presented, suggesting that the reaction type is a deflagration rather than a detonation. A strong plume of flame is emitted from the surface, indicating the potential for this material to perform useful work either as an initiator or as a propellant. The shape of the flame front transitioned from an inverted V at thin-film thicknesses to a neat square-shaped front once the material became self-confining at 50 μm. Refereed/Peer-reviewed

Within wave energy a large challenge remains in designing a Power Take-Off (PTO) system capable of converting the slow oscillations induced by waves into electricity. Fluid power is an essential part of most PTO-concepts. To implement an efficient control of the load force produced by a cylinder on a floating body, throttle-less force control by discrete variation of the effective cylinder area has been investigated and found feasible for the Wavestar wave energy concept. However, the feasibility study assumes adequate valve performance, such that only the compression loss remains. This paper investigates the required valve performance to achieve this energy efficient operation, while meeting basic dynamic requirements. The components making up the total energy loss during shifting is identified by analytically expressing the losses from the governing differential equations. From the analysis a framework for evaluating the adequacy of a valve’s response is established, and the analysis shows the results may be normalised for a wider range of systems. Finally, the framework is successfully applied to the Wavestar converter.

Proceedings of Bath/ASME Symposium on Fluid Power and Motion Control, Bath, September 2008.

The explosive properties of porous silicon (pSi) provide an alternative to existing carbon-based explosives. Here, an investigation into these explosive properties is conducted, by introducing an oxidiser onto freshly etched pSi films with varying pore sizes as determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Explosions are triggered via the application of an electric spark. Light output and spectral data are collected to characterize the explosion. Measurements of light output indicate that sodium perchlorate produces the most brilliant explosions, however spectral data indicate that aluminium and gadolinium nitrates produce hotter explosions. The energy output is measured by means of Differential Scanning Calorimetry (DSC), indicating that almost 9 kJ/g is released, double that released by the detonation of TNT. The energetic material cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) is added to investigate a method of improving explosive performance of pSi, with disappointing results.