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This article concerns high accuracy positioning control with switching optimization for an equal coded digital valve system. Typically, pulse number modulation control cannot realize micro-positioning due to the characteristics of step-wise flow variation, therefore, a new position controller consisting of a model-based pulse number modulation and a differential pulse width modulation strategy is proposed to control the position of a hydraulic cylinder at high and low velocity cases, respectively. In addition, in order to solve several problems caused by the pulse number modulation and differential pulse width modulation, such as increased number of switchings and large difference among number of switchings of valves, a switching optimization consisting of a switching cost function, a circular buffer and a circular switching method is proposed. An adaptive weight of the switching cost function is proposed for the first time to reduce the total number of switchings under different pressure differences and its design criterion is presented. A circular buffer and a new circular switching method are used to improve the degree of equal distribution of switchings when the pulse number modulation and differential pulse width modulation are used, respectively. Comparative experimental results indicated that the average and the minimum positioning error for the proposed controller are only 10 and 1 μm, respectively. The number of switchings and the degree of equal distribution of switchings are significantly optimized. Moreover, the pressure fluctuations caused by the proposed controller remain acceptable. acceptedVersion

This study proposes a novel digital hydraulic valve system using multiple equal size on/off valves and a circulating switching control, with an aim to increase the resolution and the linearity of the digital hydraulic valve systems. The solution is founded on the equal coded valve system concept which represents a recent development in the digital hydraulic valve technology. The circulating switching control algorithm is used to overcome non-linearities occurring in the typical non-circulating switching control and to decrease the operating frequency of single on/off valves. As a result, a substantial improvement in tracking control performance is demonstrated with 8+8 parallel connected valves. The results verify that compact, robust and high-performance valve control can be realized. acceptedVersion

ITER-RH system is used to exchange the divertor’s 54 cassette assemblies in the vessel. Water hydraulics and servo valves are currently used in the task but concerns exist with robustness and availability of suitable components. An alternative option is to use digital technology where on/off valves and intelligent control is used to produce proportional output. So far, no proper high-pressure on/off valves existed in the market and therefore a new concept was developed and tested with promising results. A mock-up of the remote handling system was used as test bench. The system was simulated in order to dimension the valve system and to tune the valve controller. A complete valve package with 16 prototype on/off valves and a manifold was manufactured and long-term tests of 60 working days was conducted. A new level of performance was demonstrated throughout the tests as tracking accuracies were approximately ten times better than with servo valve. Although some design faults where detected and system had faulty components, tracking accuracy was very good. Tracking and positioning capability of digital valve system exceeds all requirements and seems applicable for ITER RH application. acceptedVersion

Artikkelissa tarkastellaan evoluutioyhtälöpohjaisen jännitysväsymismallin stokastista laajennusta. Esitetty malli on muodostettu yleisten kontinuumimekaniikan periaatteiden mukaisesti ja on siten luonnostaan moniakselinen ja käsittelee kaikki jännityskomponentit ekvivalentilla tavalla. Malli soveltuu myos mielivaltaiselle kuormitushistorialle. Esimerkkinä tarkastellaan yksinkertaista valkoisella kohinalla häirityn säännollisen kuormituksen aiheuttaman elinikäaennusteen jakaumaa. Vacuum brazed steel-copper laminate could be used in high-pressure hydraulic manifolds in order to reduce size, weight and allow use of complex designs. The durability of such material is unknown. Samples were manufactured and static and dynamic tests were conducted. Results showed reduced material performance due to heat treatment. A hydraulic test manifold was manufactured and a long-term pressure load test was conducted. The material showed surprisingly good durability and pressure hull did not break in tests. A microscopic study was performed and only solidified copper in the corners had micro cracks after 10 million test cycles. publishedVersion

Digital hydraulic valve system is a new kind of hydraulic control valve assembly, which has potential to save energy and improve performance of valve controlled actuators. The typical digital valve system has 4-6 parallel connected on/off valves per control edge totaling 16-24 valves in the four-way valve configuration. The flow capacities of the parallel connected valves are set according to the powers of two such that it is possible to achieve 2 N different flow rates with N valves. An alternative approach is to use equally sized valves, which means that N parallel connected valves give only N +1 different flow rates. This approach has several benefits, but the number of valves becomes very large. This paper shows that it is possible to implement valve assembly having 128 miniaturized valves, such that it can be installed instead of traditional CETOP3 servo or proportional valve. Careful electromagnetic optimization and mechatronic design are used together with novel manufacturing methods and new type of power electronics. The prototype is build and experimentally studied and results show that the performance of this kind of digital valve system is superior to traditional four-way control valves in terms of response time and fault tolerance.

Previous research on digital fluid power indicates down-scaling to be beneficial to the characteristics of digital valves. This theoretical aspect yields to use equal size on/off valves in digital hydraulic valve systems. A simple miniaturized on/off valve, having orifice diameter of 0.7 mm, have been developed to study the feasibility of this approach. A manifold manufacturing technology also has been developed to facilitate a compact framework for the valve system containing dozens of the miniature valves. The first equal coded valve system prototype contains 16 miniature valve prototypes. A natural modulation method for an equal coded valve system is Pulse Number Modulation (PNM), where the output depends on the number of activated valves. With this modulation method, resolution of the output is equivalent to the number of the valves in the control edge. Limited resolution hampers the tracking control performance especially at low velocity where small steps in flow rate are required. The main purpose of this paper is to study the feasibility of Pulse Frequency Modulation (PFM) to improve the controllability of the equal coded valve system at the velocities below the minimum velocity of PNM control. Poor controllability at low velocities is one of the main challenges of the digital hydraulic valve systems. Characteristics of the PFM method are analysed and an experimental study is carried out to measure the improvement of the PFM method on the tracking control performance. The study indicates that the PFM method is an effective way to improve tracking control performance at low velocity.

Water hydraulics is an interesting alternative to oil hydraulics since it uses a clean, environment friendly, and non-inflammable pressure medium. However, the availability of good control valves, which are essential components in many hydraulic systems, is limited in water hydraulics owing to the challenging characteristics of water. This, in turn, considerably limits the application of water hydraulics. In this thesis, a new digital hydraulic valve technology is investigated in order to promote the applicability of this clean technology; the method using equal-size on/off valves is preferred.This equal coding method suffers from a lack of suitable valves. Thus, a fast-acting and low-power-consuming miniature valve is developed. The valve development is based on previous experience with oil hydraulic miniature valves and is carried out mainly with heuristic methods, by using simplified electromagnetic equations and scaling. However, the prototypes show good properties for the intended purpose. As another challenge, a high number of these valves are needed in order to achieve sufficient resolution for demanding control. To decrease this requirement, the circulating switching control method is proposed, which can increase the effective flow resolution of the valve system using the existing valves. The method divides the switching duty equally among the valves and can diminish the drawbacks that exist in typical non-circulating switching control.As the main goal, a water hydraulic servo axis was implemented using the developed miniature valves and the control method. The control system comprises a simple model based valve controller as the lower level part and a filtered P-controller as the upper level motion controller. Excellent tracking and positioning accuracy was achieved with a valve system having 16 miniature valves in total and using this relatively simple controller structure. This verifies that high-performance water hydraulic motion control can be realized with a reasonable effort using on/off seat valves. This gives hope for increasing the applicability of water hydraulics.