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Designing Fast Switching Valves (FSVs) for digital displacement units is a complicated process pushing the technology to the limit. The system dynamics and the interaction of the fluid, mechanical structure, actuator and control hence calls for advanced modelling, including CFD and FEA, to capture, e.g. fluid stiction effects, end-damping and impact contact stresses. Unfortunately, this essentially renders optimization processes infeasible due to the computational burden involved, although this is precisely what is required for this type of complex multi-domain problem. Therefore, the focus of the current article is on how a complex mechatronic design problem, like designing an FSV, may be aided by considering decomposing and simplification through sensitivity analysis and analyzing correlations between the design and output parameters. This is done to significantly reduce the original design problem without compromising the investigated design space. The paper focuses specifically on the results related to an FSV and the flow delivering part of this, showing the influence of the various design parameters. However, the approach and considerations may be generalized to an other areas as well.

Hydraulic servo systems are characterized by nonlinear dynamics that can render control design challenges. Controllers for a linearized model will typically be conservative, and the stability of the closed loop system, in the Lyapunov sense, may be difficult to prove. On the contrary, the backstepping technique can lead to control algorithms for which stability margins can be estimated. However, these tend to be complex algorithms that are difficult to apply. In this paper, the backstepping control design procedure is applied to a hydraulically actuated robot. A sliding mode disturbance observer is utilized to avoid the high complexity of the backstepping algorithm. The paper’s primary focus is hence on proving the stability of the proposed algorithm and its applicability to a laboratory setup. However, ways to improve performance are also discussed. Finally, results are presented where the designed controller is tested in both simulations and applied to the laboratory setup, and compared to linear controllers.

Fluid power: digital, reliable, sustainable : 13th International Fluid Power Conference : 13th-15th June 2022 : proceedings — Open Access version / Editor: Katharina Schmitz 13. International Fluid Power Conference, IFK 2022, Aachen, Germany, 13 Jun 2022 - 15 Jun 2022; Aachen : RWTH Aachen University 129-147 (2023)., Published by RWTH Aachen University, Aachen

Winch systems have a critical role in offshore operations as they are widely used in various applications. Hydraulic drives have been preferred for these systems, though currently, there is an increasing trend to replace them with fully electrical systems, mainly due to the higher energy efficiency they offer. However, hydraulic winch drives have several characteristics, such as robustness and the ability to produce large torques for their size, which are attractive to the offshore industry. This paper provides an analytical review of offshore winch drive topologies and their corresponding control techniques. Based on the reviewed articles, some literature gaps are identified, and several suggestions for future research are given.

Digital Displacement Machines (DDM) have been shown to improve energy efficiency for various applications such as wind turbine and automotive transmission systems. A DDM’s performance depends heavily on the digital valves that it utilizes. This paper investigates the required digital valve flow coefficient and switching time for realizing a digital offshore winch drive. The proposed drive improves system efficiency and reliability by replacing the winch’s conventional hydraulic motors with DDMs and removing the gearboxes. A commercially available winch system of an offshore knuckle-boom crane is used as an example when deriving the parameters of the DDM. The valve specifications are derived conservatively based on simulations to ensure a motor efficiency of at least 90 % throughout the operating range of the winch. A partial-stroke strategy is used to control the motor displacement where the highpressure valve can be closed at any given shaft angle before the cylinder reaches the top dead center. It is concluded that commercially available valves will require a DDM with a high number of cylinders, resulting in a complex system with high cost. On the contrary, certain prototype valves have shown promise for enabling the use of DDM with as few as seven pistons. However, further experimental work is required to verify the performance of these valves.

In this paper, a new methodology is presented to estimate the lifetime impact of design changes, called Failure Likelihood Assessment (FLA). The discussion in this paper is on the fatigue lifetime prediction of axial piston units, especially after a design change. The demonstration object is an axial piston pump due to extreme environmental conditions and high specification demands, where the FLA is applied to a manufacturing change in an existing product and delivers an effect on the unit reliability. The resulted reliability imp rovement, if combined with typical calculation methods like Weibull analysis, delivers an increase in predicted lifetime considering the intended modification. As demonstration subje ct, a change of the manufacturing process of the cylinder block hub in an axial piston pump is used. The effect to the lifetime is predicted via the FLA-method and the results are calculated with test data and compared to theoretical results. The paper shows that the methodology delivers highly accurate results providing that the FLA is a powerful tool to analyze design changes as weil as new designs in regard to reliability and lifetime. The benefit for the user of this methodology will hence be more reliable products with optimized designs tobest fulfil customer's performance requirements.